Composite powder containing calcium carbonate and having microstructured particles

ABSTRACT

A composite powder containing microstructured particles obtainable by means of a method in which large particles are combined with small particles, wherein
         the large particles have an average particle diameter within the range from 0.1 μm to 10 mm,   the large particles comprise at least one polymer,   the small particles are arranged on the surface of the large particles and/or distributed inhomogeneously within the large particles,   the small particles comprise sphere-shaped precipitated calcium carbonate particles having an average diameter within the range from 0.05 μm to 50.0 μm, wherein the sphere-shaped calcium carbonate particles are obtainable by means of a method in which
 
a. a calcium hydroxide suspension is initially charged,
 
b. carbon dioxide or a carbon dioxide-containing gas mixture is introduced into the suspension from step a. and
 
c. resultant calcium carbonate particles are separated off,
 
with 0.3% by weight to 0.7% by weight of at least one aminotrisalkylenephosphonic acid being further added.
       

     Preferred application areas of the composite powder encompass its use as additive, especially as polymer additive, as additive substance or starting material for compounding, for the production of components, for applications in medical technology and/or in microtechnology and/or for the production of foamed articles. 
     The invention therefore also provides components obtainable by selective laser sintering of a composition comprising a composite powder according to the invention, except for implants for uses in the field of neurosurgery, oral surgery, jaw surgery, facial surgery, neck surgery, nose surgery and ear surgery as well as hand surgery, foot surgery, thorax surgery, rib surgery and shoulder surgery. 
     The invention also provides the sphere-shaped calcium carbonate particles which can advantageously be used to produce the composite particles according to the invention, and the use thereof.

The present invention relates to a calcium carbonate-containingcomposite powder containing microstructured particles, method forproduction thereof, use thereof and also components obtainable byselective laser sintering, except for implants for uses in the field ofneurosurgery, oral surgery, jaw surgery, facial surgery, neck surgery,nose surgery and ear surgery as well as hand surgery, foot surgery,thorax surgery, rib surgery and shoulder surgery.

Calcium carbonate, CaCO₃, is a carbonic-acid calcium salt which isnowadays used in many areas of daily life. In particular, it is used asadditive or modifier in paper, paints, plastics, inks, adhesives andpharmaceuticals. In plastics, calcium carbonate primarily serves asfiller to replace the comparatively expensive polymer.

Composites, too, are already known and refer to a material composed oftwo or more combined materials that has different material propertiescompared to its individual components. What are important for theproperties of composites are the material properties and the geometry ofthe components. In particular, size effects are often significant.Combination is generally achieved by integral bonding or form-fitting ora mix of the two.

Furthermore, microstructured composite particles containing calciumsalts, especially calcium carbonate, are also already known per se.

For instance, WO 2012/126600 A2 discloses microstructured compositeparticles obtainable by means of a method in which large particles arecombined with small particles, wherein

-   -   the large particles have an average particle diameter within the        range from 0.1 μm to 10 mm,    -   the average particle diameter of the small particles is not more        than 1/10 of the average particle diameter of the large        particles,    -   the large particles comprise at least one polymer,    -   the small particles comprise calcium carbonate,    -   the small particles are arranged on the surface of the large        particles and/or distributed inhomogeneously within the large        particles,        wherein the small particles comprise precipitated calcium        carbonate particles having an average particle size within the        range from 0.01 μm to 1.0 mm.

Furthermore, WO 2012/126600 A2 describes microstructured compositeparticles obtainable by means of a method in which large particles arecombined with small particles, wherein

-   -   the large particles have an average particle diameter within the        range from 0.1 μm to 10 mm,    -   the average particle diameter of the small particles is not more        than 1/10 of the average particle diameter of the large        particles,    -   the large particles comprise at least one polymer,    -   the small particles comprise at least one calcium salt,    -   the small particles are arranged on the surface of the large        particles and/or distributed inhomogeneously within the large        particles,        wherein the large particles comprise at least one resorbable        polyester having a number-average molecular weight within the        range from 500 g/mol to 1 000 000 g/mol.

The composite particles shown in WO 2012/126600 A2 are said to beespecially suitable as additive, especially as polymer additive, asadditive substance or starting material for the production ofcomponents, for applications in medical technology and/or inmicrotechnology and/or for the production of foamed articles. The methodof selective laser sintering (0 method) is mentioned, inter alia, inthat document.

However, materials better suited to selective laser sintering aredesirable. One disadvantage of the composite particles of WO 2012/126600A2 is in particular their poor pourability, which can be reduced onlypartially, even by using pouring aids. Especially for the production ofimplants, additions of such pouring aids are not advantageous, sincethey generally adversely affect the properties of the resultant implant,especially its biological compatibility and biodegradability.Furthermore, the poor pourability complicates transport in the lasersintering system.

When producing components by laser sintering using the materials of WO2012/126600 A2, the following additional problems occur. Although it ispossible to carry out sintering of ground composite particles, thesurface quality and surface nature as well as the component density ofthe resultant components is not completely satisfactory. What would bedesirable would be in particular a better shrinkage behavior and animproved dimensional stability of the resultant components as well as abetter heat-conductivity behavior outside the laser-treated region.Furthermore, a more efficient method of producing components would bedesirable.

U.S. Pat. No. 4,915,884 A relates to a method for producing a granularmaterial for water treatment, allowing the production of granules havinga specific gravity d and a size t, which can be adjusted independentlyof one another within the range of 1<d≤3 and 0.5 mm≤t≤10 mm in order tobe able to adapt the granules to the treatment type for which thematerial is intended to be used. The method comprises the formation of amixture composed of an oxidizable thermoplastic resin having a specificgravity dr less than d and an adjuvant in the form of a powder having agranulometry less than about 200 μm and a specific gravity da meetingthe requirement da>1.7 d-0.7 dr, it being intended that the proportionby weight of the adjuvant pa meet a specific requirement. The mixture isheated into the plastic state, and extruded to form cylindrical strandswhich are immediately cut into plastic pieces which are shorter thantheir diameter. The plastic pieces are solidified to form sphericalgranules and their surface is subjected to oxidation to form hydrophilicsites.

Optionally, a cationic polyelectrolyte is grafted onto the surface ofthe granules.

The thermoplastic resin used is, for example, HDPE.

The adjuvant used is, for example, calcium carbonate having an averageparticle size of 30 μm and a specific gravity of 2.71.

The oxidation is, for example, achieved with a mixture composed ofsulfuric acid and potassium bichromate.

However, it is not possible to gather from this publication anyindication of sphere-shaped calcium carbonate particles.

Against this background, it is an object of the present invention toshow ways of providing a calcium carbonate-containing composite powderhaving improved properties. In particular, a material having improvedlaser sintering properties is to be provided, which material has inparticular an improved pourability, allows in the case of lasersintering the production of components having improved surface qualityand surface nature as well as improved component density, and exhibitsin particular better shrinkage behavior and an improved dimensionalstability of the resultant components as well as a betterheat-conductivity behavior outside the laser-treated region. Inaddition, a more efficient method of producing components is desired.Lastly, it is also a goal of the present invention to provideparticularly advantageous components. Furthermore, solvent-free productswhich can be used without any difficulties especially in areas withrestrictions regarding the presence of solvent residues in the productare striven for. What should be especially highlighted in this contextare products for medical technology applications, which must generallybe completely solvent-free. Lastly, ways of optimally preventing thermaldegradation, especially polymer degradation, during the production ofthe end products are also sought after.

These objects, and further objects which are not specifically mentionedand which can be directly derived from the above contexts, are achievedby the provision of a composite powder containing microstructuredparticles having all the features of the present claim 1. The dependentclaims which refer back to claim 1 describe particularly expedient usevariants of the composite powder. The use claim relates to aparticularly expedient application of the composite powder according tothe invention. Furthermore, protection is given to a particularlyadvantageous component obtainable by selective laser sintering of acomposition containing a composite powder according to the invention,except for implants for uses in the field of neurosurgery, oral surgery,jaw surgery, facial surgery, neck surgery, nose surgery and ear surgeryas well as hand surgery, foot surgery, thorax surgery, rib surgery andshoulder surgery. The invention also provides the sphere-shaped calciumcarbonate particles which can advantageously be used to produce thecomposite particles according to the invention, and the use thereof.

By providing a composite powder containing microstructured particlesobtainable by means of a method in which large particles are combinedwith small particles, wherein

-   -   the large particles have an average particle diameter within the        range from 0.1 μm to 10 mm,    -   the large particles comprise at least one polymer,    -   the small particles are arranged on the surface of the large        particles and/or distributed inhomogeneously within the large        particles,    -   the small particles comprise sphere-shaped precipitated calcium        carbonate particles having an average diameter within the range        from 0.05 μm to 50.0 μm, preferably within the range from 2.5 μm        to 30.0 μm,

wherein the sphere-shaped calcium carbonate particles are obtainable bymeans of a method in which

a. a calcium hydroxide suspension is initially charged,

b. carbon dioxide or a carbon dioxide-containing gas mixture isintroduced into the suspension from step a. and

c. resultant calcium carbonate particles are separated off,

with 0.3% by weight to 0.7% by weight of at least oneaminotrisalkylenephosphonic acid being further added, it is possible tomake available, in a not readily foreseeable manner, a calciumcarbonate-containing composite powder having improved properties, whichare in particular outstandingly suitable for use in laser sinteringmethods. The composite powder according to the invention has an improvedpourability, allows in the case of laser sintering the production ofcomponents having improved surface quality and surface nature as well asimproved component density. At the same time, the resultant componentsexhibit in particular a better shrinkage behavior and an improveddimensional stability. Furthermore, a better heat-conductivity behavioroutside the laser-treated region can be established.

Furthermore, the composite powder according to the invention allows amore efficient production of components, especially by the lasersintering method. The melt flow of the melt obtainable using thecomposite powder according to the invention is distinctly increased(improved). In comparison with conventional materials, the compositepowder according to the invention is in particular better processable bythe SLM method and allows a distinctly better layer structure in the SLMmethod. The components obtainable by the SLM method using the compositepowder according to the invention are distinguished by an extremely highquality and have, in comparison with components produced by the SLMmethod using conventional materials, distinctly fewer imperfections, ahigher component density, preferably greater than 95% and in particulargreater than 97%, and a lower porosity. At the same time, the amount ofdegradation products in the resultant components is distinctly lower andthe cell compatibility of the components is extremely high.

The other properties of the components obtainable in this way isexcellent, too. The components have very good mechanical properties anda very good pH stability. At the same time, the biological compatibilityof the components is distinctly improved. Comparable products are notobtainable using the pure polymers, all the more because correspondingpolymer powders that could be processed by the SLM method are not known.

A further advantage of the present invention can be considered that ofbeing able to specifically control and adjust the properties of thecomposite powder according to the invention, especially the flowproperties of the composite powder, via the use amounts and theproperties of the large particles and of the small particles, especiallyvia the properties of the calcium carbonate particles, particularly viathe particle size of the calcium carbonate particles, and via the amountof calcium carbonate particles. Furthermore, by classification of thecomposite powder, it is possible for especially the calcium carbonatecontent of the composite powder and the flow properties of the compositepowder to be altered and to be specifically tailored to the particularintended application.

Especially in combination with polylactide as polymer, the followingadvantages arise according to the invention.

Using the composite powder according to the invention, it is possible togenerate degradable implants having controllable resorption kinetics andadjustable mechanical properties. Polylactides, which are preferablypresent in the composite powder, are biodegradable polymers based onlactic acid. In organisms, polylactides are degraded by hydrolysis.Calcium salts, especially calcium phosphate and calcium carbonate, aremineral materials based on calcium and are degraded in the body by thebone's natural regeneration process. Calcium carbonate has theparticularly advantageous property of buffering the acidic environmentin the case of polylactide degradation, which environment is sometimestoxic for bone cells. In comparison with calcium phosphate (pH 4),calcium carbonate already buffers at a pH of approx. 7, i.e., close tothe physiological value of 7.4. Via the molecular-chain length and thechemical composition of the polymer, especially of the polylactide, itis possible to adjust the time until complete degradation. A similaradjustment is possible for the mechanical properties of the polymer.

The composite powder according to the invention can be processed withthe aid of the additive manufacturing process selective laser melting(SLM) to form implant structures. Here, a specific tailoring of materialand manufacturing process to one another and to the medical requirementsis possible. The utilization of additive manufacturing and of theassociated geometrical freedom offers the possibility of providing theimplant with an inner and open pore structure which meets the wishes ofthe surgeon and which ensures that the implant is supplied throughout.Furthermore, implants individually tailored by means of additivemanufacturing, as required for the treatment of large-area bone defectsin the facial and skull region, can be produced rapidly andeconomically. The advantage of the composite powder according to theinvention for SLM processing is, in particular, that the polymer can bemelted by the laser radiation at relatively low temperatures, preferablyless than 300° C., and the calcium carbonate particles remain thermallystable at said temperatures. Through tailored synthesis of the compositepowder according to the invention, the calcium carbonate particles canthus be embedded homogeneously in the entire volume of the implant in apolylactide matrix without thermal damage due to the laser radiation.The strength of the implant is determined, firstly, by the polylactidematrix and, secondly, by the morphology of the calcium carbonateparticles, and preferably also by the mixture ratio of the componentsused. Moreover, the implants are bioactive, since they, via the choiceof material and the subsequent coating with a growth-stimulating protein(rhBMP-2), induce the surrounding bone tissue in an active manner tobuild bone and to replace the scaffolding structure (implant).

The major advantages of the implants additively manufactured by means ofSLM and composed of the composite powder according to the invention arein particular:

-   -   With the use of biodegradable, osteoconductive materials, there        is active stimulation of bone growth through the implant and,        even in the case of large-area defects, complete degradation is        achieved coupled with complete bone regeneration in the bone        defect to be treated. Owing to the interconnecting pore        structure, the BMP coating can have an active effect in the        entire “volume” of the implant.    -   Inward sprouting of bone tissue: The introduction of a suitable        pore structure promotes the inward sprouting of new bone tissue        into the implant. By means of the additive manufacturing        process, it is possible to introduce a defined pore structure        into the components in a reproducible manner.    -   The proposed solution further offers the advantage of optimally        preventing medical complications of long-term implants, of        optimally improving the patient's well-being through the        avoidance of a permanent foreign-body sensation and—especially        in the case of children and juveniles—of optimally realizing a        “co-growing” implant.    -   Optimum buffering: Through the use of calcium carbonate, the        acidic degradation of the material polylactide is already        buffered at a pH of approx. 7, meaning that the resultant acidic        environment surrounding the implant and thus an inflammatory or        cytotoxic effect can be avoided. Furthermore, degradation        processes of the polymer, especially of the lactic acid polymer,        are optimally suppressed.    -   High strength: The SLM process generates a complete fused        composite and thus a high component density and strength, the        result being that it is also possible to treat large-area        defects with individually tailored implants composed of a        biodegradable material and open pore structure.

Furthermore, the products according to the invention can be producedwithout the use of conventional solvents and are therefore preferablydistinguished by this “freedom from solvent”. This allows their useespecially in areas with restrictions regarding the presence of solventresidues in the product, since the products according to the inventioncan be used without any difficulties here. What should be especiallyhighlighted in this context are medical technology applications, whichmust generally be completely solvent-free. Lastly, the composite powderaccording to the invention can be processed further in a comparativelysimple manner to form the desired end products. A thermal degradation,especially polymer degradation, during the production of the endproducts is optimally prevented.

Accordingly, the present invention provides composite powders containingmicrostructured particles obtainable by means of a method in which largeparticles are combined with small particles.

In the present invention, the microscopic properties of a material arereferred to as microstructure. They include the resolvable finestructure and the grain structure. They are not present in liquids andgases. In this case, the individual atoms or molecules are present in anonordered state. Amorphous solids have in most cases a structuralshort-range order in the region of adjacent atoms, but not a long-rangeorder. By contrast, crystalline solids have an ordered lattice structurenot only in the short-range region, but also in the long-range region.

Within the context of the present invention, the large particlescomprise at least one polymer, which polymer is fundamentally notsubject to any further restrictions. However, the polymer is preferablya thermoplastic polymer, expediently a biopolymer, a rubber, especiallynatural rubber or synthetic rubber, and/or a polyurethane.

In this context, the term “thermoplastic polymer” refers to a plasticwhich can be deformed (thermoplastically) within a certain temperaturerange, preferably within the range from 25° C. to 350° C. This processis reversible, i.e., it can be repeated as often as desired throughcooling and reheating right into the molten state, so long as so-calledthermal decomposition of the material does not commence as a result ofoverheating. This distinguishes thermoplastic polymers from thethermosets and elastomers.

The term “biopolymer” refers to a material which consists of biogenicraw materials (renewable raw materials) and/or is biodegradable(biogenic and/or biodegradable polymer). Said term thus covers biobasedbiopolymers which are biodegradable or else not biodegradable as well aspetroleum-based polymers which are biodegradable. This provides adelimitation with respect to the conventional, petroleum-based materialsor plastics which are not biodegradable, such as, for example,polyethylene (PE), polypropylene (PP) and polyvinyl chloride (PVC).

The term “rubber” refers to a high-molecular-weight, uncrosslinkedpolymeric material having rubber-elastic properties at room temperature(25° C.). At higher temperatures or under the influence of deformationforces, a rubber exhibits an increasing viscous flow and thus allows itsreshaping under suitable conditions.

Rubber-elastic behavior is characterized by a relatively low shearmodulus with a rather low temperature dependence. It is caused bychanges in entropy. As a result of stretching, the rubber-elasticmaterial is forced into a more ordered configuration, which leads to adecrease in entropy. After removal of the force, the polymers thereforereturn to their original position and entropy goes back up.

The term “polyurethane” (PU, DIN [German Institute for Standardization]abbreviation: PUR) refers to a plastic or a synthetic resin, each ofwhich arises from the polyaddition reaction of diols or polyols withpolyisocyanates. Characteristic of a polyurethane is the urethane group.

Within the context of the present invention, particular preference isgiven to using thermoplastic polymers. In this connection, particularlysuitable polymers include the following polymers:acrylonitrile-ethylene-propylene-(diene)-styrene copolymer,acrylonitrile-methacrylate copolymer, acrylonitrile-methyl methacrylatecopolymer, acrylonitrile-chlorinated polyethylene-styrene copolymer,acrylonitrile-butadiene-styrene copolymer,acrylonitrile-ethylene-propylene-styrene copolymer, aromatic polyesters,acrylonitrile-styrene-acrylic ester copolymer, butadiene-styrenecopolymer, cellulose acetate, cellulose acetate butyrate, celluloseacetate propionate, hydrogenated cellulose, carboxymethylcellulose,cellulose nitrate, cellulose propionate, cellulose triacetate, polyvinylchloride, ethylene-acrylic acid copolymer, ethylene-butyl acrylatecopolymer, ethylene-chlorotrifluoroethylene copolymer, ethylene-ethylacrylate copolymer, ethylene-methacrylate copolymer,ethylene-methacrylic acid copolymer, ethylene-tetrafluoroethylenecopolymer, ethylene-vinyl alcohol copolymer, ethylene-butene copolymer,ethylcellulose, polystyrene, polyfluoroethylenepropylene, methylmethacrylate-acrylonitrile-butadiene-styrene copolymer, methylmethacrylate-butadiene-styrene copolymer, methylcellulose, polyamide 11,polyamide 12, polyamide 46, polyamide 6, polyamide 6-3-T, polyamide6-terephthalic acid copolymer, polyamide 66, polyamide 69, polyamide610, polyamide 612, polyamide 61, polyamide MXD6, polyamide PDA-T,polyamide, polyaryl ether, polyaryl ether ketone, polyamide imide,polyacrylamide, polyaminobismaleimide, polyarylates, polybutene-1,polybutyl acrylate, polybenzimidazole, polybismaleimide,polyoxadiazobenzimidazole, polybutylene terephthalate, polycarbonate,polychlorotrifluoroethylene, polyethylene, polyester carbonate, polyarylether ketone, polyether ether ketone, polyether imide, polyether ketone,polyethylene oxide, polyaryl ether sulfone, polyethylene terephthalate,polyimide, polyisobutylene, polyisocyanurate, polyimide sulfone,polymethacrylimide, polymethacrylate, poly-4-methyl-1-pentene,polyacetal, polypropylene, polyphenylene oxide, polypropylene oxide,polyphenylene sulfide, polyphenylene sulfone, polystyrene, polysulfone,polytetrafluoroethylene, polyurethane, polyvinyl acetate, polyvinylalcohol, polyvinyl butyral, polyvinyl chloride, polyvinylidene chloride,polyvinylidene fluoride, polyvinyl fluoride, polyvinyl methyl ether,polyvinylpyrrolidone, styrene-butadiene copolymer, styrene-isoprenecopolymer, styrene-maleic anhydride copolymer, styrene-maleicanhydride-butadiene copolymer, styrene-methyl methacrylate copolymer,styrene-methylstyrene copolymer, styrene-acrylonitrile copolymer, vinylchloride-ethylene copolymer, vinyl chloride-methacrylate copolymer,vinyl chloride-maleic anhydride copolymer, vinyl chloride-maleimidecopolymer, vinyl chloride-methyl methacrylate copolymer, vinylchloride-octylacrylate copolymer, vinyl chloride-vinyl acetatecopolymer, vinyl chloride-vinylidene chloride copolymer and vinylchloride-vinylidene chloride-acrylonitrile copolymer.

Furthermore, the use of the following rubbers is also particularlyadvantageous: naturally occurring polyisoprene, especiallycis-1,4-polyisoprene (natural rubber; NR) and trans-1,4-polyisoprene(gutta-percha), particularly natural rubber; nitrile rubber (copolymerof butadiene and acrylonitrile; poly(acrylonitrile-co-1,3-butadiene;NBR; so-called Buna-N rubber); butadiene rubber (polybutadiene; BR);acrylic rubber (polyacrylic rubber; ACM, ABR); fluororubber (FPM);styrene-butadiene rubber (copolymer of styrene and butadiene; SBR);styrene-isoprene-butadiene rubber (copolymer of styrene, isoprene andbutadiene; SIBR); polybutadiene; synthetic isoprene rubber(polyisoprene; IR); ethylene-propylene rubber (copolymer of ethylene andpropylene; EPM); ethylene-propylene-diene rubber (terpolymer ofethylene, propylene and a diene component; EPDM); butyl rubber(copolymer of isobutylene and isoprene; IIR); ethylene-vinyl acetaterubber (copolymer of ethylene and vinyl acetate; EVM); ethylene-methylacrylate rubber (copolymer of ethylene and methyl acrylate; AEM); epoxyrubber, such as polychloromethyloxirane (epichlorohydrin polymer; CO),ethylene oxide (oxirane)-chloromethyloxirane (epichlorohydrin polymer;ECO), epichlorohydrin-ethylene oxide-allyl glycidyl ether terpolymer(GECO), epichlorohydrin-allyl glycidyl ether copolymer (GCO) andpropylene oxide-allyl glycidyl ether copolymer (GPO); polynorbornenerubber (polymer of bicyclo[2.2.1]hept-2-ene (2-norbornene); PNR);polyalkenylene (polymer of cycloolefins); silicone rubber (Q), such assilicone rubber only with methyl substituents on the polymer chain (MQ;e.g., dimethylpolysiloxane), silicone rubber with methylvinyl and vinylsubstituent groups on the polymer chain (VMQ), silicone rubber withphenyl and methyl substituents on the polymer chain (PMQ), siliconerubber with fluoro and methyl groups on the polymer chain (FMQ),silicone rubber with fluoro, methyl and vinyl substituents on thepolymer chain (FVMQ); polyurethane rubber; thiokol rubber; halobutylrubber, such as bromobutyl rubber (BIIR) and chlorobutyl rubber (CIIR);chloropolyethylene (CM); chlorosulfonyl polyethylene (CSM); hydrogenatednitrile rubber (HNBR); and polyphosphazene.

Particularly preferred nitrile rubbers include random terpolymers ofacrylonitrile, butadiene and a carboxylic acid, such as methacrylicacid. In this context, the nitrile rubber preferably comprises, based onthe total weight of the polymer, the following main components: 15.0% byweight to 42.0% by weight of acrylonitrile polymer; 1.0% by weight to10.0% by weight of carboxylic acid and the rest is predominantlybutadiene (e.g., 38.0% by weight to 75.0% by weight). Typically, thecomposition is: 20.0% by weight to 40.0% by weight of acrylonitrilepolymer, 3.0% by weight to 8.0% by weight of carboxylic acid and 40.0%by weight to 65.0% by weight or 67.0% by weight are butadiene.Particularly preferred nitrile rubbers include a terpolymer ofacrylonitrile, butadiene and a carboxylic acid, in which terpolymer theacrylonitrile content is less than 35.0% by weight and the carboxylicacid content is less than 10.0% by weight, with the butadiene contentcorresponding to the remaining rest. Even more preferred nitrile rubberscan comprise the following amounts: 20.0% by weight to 30.0% by weightof acrylonitrile polymer, 4.0% by weight to 6.0% by weight of carboxylicacid and the rest is predominantly butadiene.

The use of nitrogenous polymers, especially of polyamides, isparticularly favorable within the context of the present invention.Particular preference is given to polyamide 11, polyamide 12, polyamide46, polyamide 6, polyamide 6-3-T, polyamide 6-terephthalic acidcopolymer, polyamide 66, polyamide 69, polyamide 610, polyamide 612,polyamide 61, polyamide MXD6 and/or polyamide PDA-T, especiallypolyamide 12.

Furthermore, ultra-high-molecular-weight polyethylenes (UHMWPE) are alsoparticularly advantageous for the purposes of the present invention,especially those having an average molar mass greater than 1000 kg/mol,preferably greater than 2000 kg/mol, particularly preferably greaterthan 3000 kg/mol and in particular greater than 5000 kg/mol. In thisconnection, the average molecular weight is favorably not more than 10000 kg/mol. The density of particularly suitableultra-high-molecular-weight polyethylenes is within the range of0.94-0.99 g/cm³. The crystallinity of particularly suitableultra-high-molecular-weight polyethylenes is within the range from 50%to 90%. The tensile strength of particularly suitableultra-high-molecular-weight polyethylenes is within the range from 30N/mm² to 50 N/mm². The tensile elastic modulus of particularly suitableultra-high-molecular-weight polyethylenes is within the range from 800N/mm² to 2700 N/mm². The melting range of particularly suitableultra-high-molecular-weight polyethylenes is within the range from 135°C. to 155° C.

Furthermore, the use of resorbable polymers is also particularlyexpedient. The term “resorption” (Latin: resorbere=“absorb”) isunderstood to mean the uptake of substances in biological systems,especially into the human organism. Of interest here are especiallythose materials which can be used for the production of resorbableimplants.

Resorbable polymers which are particularly preferred according to theinvention comprise repeat units of lactic acid, of hydroxybutyric acidand/or of glycolic acid, preferably of lactic acid and/or of glycolicacid, in particular of lactic acid. Polylactic acids are particularlypreferred in this connection.

“Polylactic acid” (polylactides) are understood here to mean polymerswhich are constructed from lactic acid units. Such polylactic acids areusually produced by condensation of lactic acids, but are also obtainedin the ring-opening polymerization of lactides under suitableconditions.

Resorbable polymers which are particularly suitable according to theinvention include poly(glycolide-co-L-lactide), poly(L-lactide),poly(L-lactide-co-ε-caprolactone), poly(L-lactide-co-glycolide),poly(L-lactide-co-D,L-lactide), poly(D,L-lactide-co-glycolide) andpoly(dioxanone), with lactic acid polymers, especially poly-D-, poly-L-or poly-D,L-lactic acids, particularly poly-L-lactic acids (PLLA) andpoly-D,L-lactic acids, being very particularly preferred according tothe invention, with especially the use of poly-L-lactic acids (PLLA)being very particularly advantageous.

According to the invention, poly-L-lactic acid (PLLA) preferably has thefollowing structure

where n is a whole number, preferably greater than 10.

Poly-D,L-lactic acid preferably has the following structure

where n is a whole number, preferably greater than 10.

Lactic acid polymers suitable for the purposes of the present inventionare, for example, commercially available from Evonik Nutrition & CareGmbH under the trade names Resomer® GL 903, Resomer® L 206 S, Resomer® L207 S, Resomer® R 208 G, Resomer® L 209 S, Resomer® L 210, Resomer® L210 S, Resomer® LC 703 S, Resomer® LG 824 S, Resomer® LG 855 S, Resomer®LG 857 S, Resomer® LR 704 S, Resomer® LR 706 S, Resomer® LR 708,Resomer® LR 927 S, Resomer® RG 509 S and Resomer® X 206 S.

Resorbable polymers which are particularly advantageous for the purposesof the present invention, these being preferably resorbable polyesters,by preference lactic acid polymers, particularly preferably poly-D-,poly-L- or poly-D,L-lactic acids and in particular poly-L-lactic acids,have a number-average molecular weight (Mn), preferably determined bygel-permeation chromatography against narrow-distribution polystyrenestandards or by end-group titration, greater than 500 g/mol, preferablygreater than 1000 g/mol, particularly preferably greater than 5000g/mol, expediently greater than 10 000 g/mol and in particular greaterthan 25 000 g/mol. On the other hand, the number average of preferredresorbable polymers is less than 1 000 000 g/mol, expediently less than500 000 g/mol, favorably less than 100 000 g/mol and in particular notmore than 50 000 g/mol. A number-average molecular weight within therange from 500 g/mol to 50 000 g/mol has been found to very particularlyeffective within the context of the present invention.

The weight-average molecular weight (Mw) of preferred resorbablepolymers, these being by preference resorbable polyesters, favorablylactic acid polymers, particularly preferably poly-D-, poly-L- orpoly-D,L-lactic acids and in particular poly-L-lactic acids, preferablydetermined by gel-permeation chromatography against narrow-distributionpolystyrene standards, is by preference within the range from 750 g/molto 5 000 000 g/mol, preferably within the range from 750 g/mol to 1 000000 g/mol, particularly preferably within the range from 750 g/mol to500 000 g/mol and in particular within the range from 750 g/mol to 250000 g/mol, and the polydispersity of said polymers is favorably withinthe range from 1.5 to 5.

The inherent viscosity of particularly suitable resorbable polymers,these being preferably lactic acid polymers, particularly preferablypoly-D-, poly-L- or poly-D,L-lactic acids and in particularpoly-L-lactic acids, measured in chloroform at 25° C. and 0.1% polymerconcentration, is within the range from 0.3 dL/g to 8.0 dL/g, preferablywithin the range from 0.5 dL/g to 7.0 dL/g, particularly preferablywithin the range from 0.8 dL/g to 2.0 dL/g and in particular within therange from 0.8 dL/g to 1.2 dL/g.

Furthermore, the inherent viscosity of particularly suitable resorbablepolymers, these being preferably lactic acid polymers, particularlypreferably poly-D-, poly-L- or poly-D,L-lactic acids and in particularpoly-L-lactic acids, measured in hexafluoro-2-propanol at 30° C. and0.1% polymer concentration, is within the range from 1.0 dL/g to 2.6dL/g and in particular within the range from 1.3 dL/g to 2.3 dL/g.

Furthermore, what are extremely advantageous within the context of thepresent invention are polymers, favorably thermoplastic polymers,preferably lactic acid polymers, particularly preferably poly-D-,poly-L- or poly-D,L-lactic acids and in particular poly-L-lactic acids,having a glass transition temperature greater than 20° C., favorablygreater than 25° C., preferably greater than 30° C., particularlypreferably greater than 35° C. and in particular greater than 40° C.Within the context of a very particularly preferred embodiment of thepresent invention, the glass transition temperature of the polymer iswithin the range from 35° C. to 70° C., favorably within the range from55° C. to 65° C. and in particular within the range from 60° C. to 65°C.

Furthermore, what are particularly suitable are polymers, favorablythermoplastic polymers, preferably lactic acid polymers, particularlypreferably poly-D-, poly-L- or poly-D,L-lactic acids and in particularpoly-L-lactic acids, having a melting temperature greater than 50° C.,favorably of at least 60° C., preferably of greater than 150° C.,particularly preferably within the range from 130° C. to 210° C. and inparticular within the range from 175° C. to 195° C.

In this connection, the glass temperature and the melting temperature ofthe polymer is preferably ascertained by means of differential scanningcalorimetry (DSC for short). The following procedure has been found tovery particularly effective in this context:

Performance of the DSC measurement under nitrogen on a Mettler-ToledoDSC 30S. The calibration is preferably done using indium. Themeasurements are preferably carried out under dry, oxygen-free nitrogen(flow rate: preferably 40 ml/min). The sample weight is preferablychosen between 15 mg and 20 mg. The samples are first heated from 0° C.to preferably a temperature above the melting temperature of the polymerunder investigation, then cooled to 0° C. and heated a second time from0° C. to the stated temperature at a heating rate of 10° C./min.

Thermoplastic polymers which are very particularly preferred arepolyamides, UHMWPE and resorbable polymers, particularly resorbablepolyesters, such as polybutyric acid, polyglycolic acid (PGA), lacticacid polymers (PLA) and lactic acid copolymers, with lactic acidpolymers and lactic acid copolymers, in particular poly-L-lactide,poly-D,L-lactide and copolymers of D,L-PLA and PGA, having been found tobe very particularly effective according to the invention.

For the goals of the present invention, what are very particularlysuitable are especially the following polymers:

-   1) poly-L-lactide (PLLA), preferably having an inherent viscosity    within the range from 0.5 dL/g to 2.5 dL/g, favorably within the    range from 0.8 dL/g to 2.0 dL/g and in particular within the range    from 0.8 dL/g to 1.2 dL/g (measured in each case at 0.1% in    chloroform at 25° C.), preferably having a glass transition    temperature within the range from 60° C. to 65° C., further    preferably having a melting temperature within the range from    180° C. to 185° C., further preferably ester-terminated;-   2) poly(D,L-lactide), preferably having an inherent viscosity within    the range from 1.0 dL/g to 3.0 dL/g, favorably within the range from    1.5 dL/g to 2.5 dL/g and in particular within the range of 1.8-2.2    dL/g (measured in each case at 0.1% in chloroform at 25° C.),    preferably having a glass transition temperature within the range    from 55° C. to 60° C.,

with the best results being achieved using a poly-L-lactide whichpreferably has an inherent viscosity within the range from 0.5 dL/g to2.5 dL/g, favorably within the range from 0.8 dL/g to 2.0 dL/g and inparticular within the range from 0.8 dL/g to 1.2 dL/g (measured in eachcase at 0.1% in chloroform at 25° C.), preferably has a glass transitiontemperature within the range from 60° C. to 65° C., further preferablyhas a melting temperature within the range from 180° C. to 185° C. andis further preferably ester-terminated.

Within the context of the present invention, the small particles (secondmaterial) usable for the production of the composite powder according tothe invention comprise sphere-shaped precipitated calcium carbonateparticles. In contrast to other known shapes from the prior art, thecalcium carbonate particles are thus not, for example, constructed fromneedles, rhombohedrons or scalenohedrons (precipitated calciumcarbonate; PCC) or from irregularly shaped particles (ground calciumcarbonate; GCC), but from sphere-shaped precipitated particles, whichare preferably predominantly present as individual particles. However,relatively small deviations from the perfect sphere shape are accepted,provided that the properties of the particles, especially theirdispersibility, are not fundamentally changed. For instance, the surfaceof the particles can have occasional imperfections or additionaldeposits.

According to the invention, the term “sphere-shaped precipitated calciumcarbonate particles” also encompasses fragments of sphere-shapedparticles, which are, for example, obtainable by grinding of the calciumcarbonate. However, the proportion of the sphere fragments is bypreference less than 95%, preferably less than 75%, particularlypreferably less than 50% and in particular less than 25%, based in eachcase on the total amount of sphere-shaped precipitated calciumcarbonate.

The average diameter of the sphere-shaped calcium carbonate particles iswithin the range from 0.05 μm to 50.0 μm, especially within the rangefrom 2.5 μm to 30.0 μm. In this connection, the average diameter isexpediently greater than 2.5 μm, favorably greater than 3.0 μm, bypreference greater than 4.0 μm, expediently greater than 5.0 μm,expediently greater than 6.0 μm, preferably greater than 7.0 μm,particularly preferably greater than 8.0 μm, yet more preferably greaterthan 9.0 μm, very particularly preferably greater than 10.0 μm, yet morepreferably greater than 11.0 μm, particularly greater than 12.0 μm andin particular greater than 13.0 μm. Furthermore, the average particlediameter is expediently less than 30.0 μm, favorably less than 20.0 μm,preferably less than 18.0 μm, particularly preferably less than 16.0 μmand in particular less than 14.0 μm.

Within the context of the present invention, the average diameter of thecalcium carbonate particles is expediently ascertained by evaluation ofscanning electron micrographs (SEM images), with preferably onlyparticles of a size of at least 0.01 μm being taken into considerationand a number average being formed over preferably at least 20 andparticularly preferably at least 40 particles. Furthermore,sedimentation analysis methods have also been found to be particularlyeffective, with the use of a Sedigraph 5100 (Micromeritics GmbH) beingparticularly advantageous in this context.

The size distribution of the calcium carbonate particles is expedientlycomparatively narrow and preferably such that at least 90.0% by weightof all calcium carbonate particles have a particle diameter within therange of average particle diameter −30% to average particle diameter+30%.

The shape factor of the calcium carbonate particles, defined here as thequotient formed from minimum particle diameter and maximum particlediameter, is expediently greater than 0.90 and particularly preferablygreater than 0.95 for at least 90% and favorably for at least 95% of allparticles. In this context, what are taken into consideration arepreferably only particles having a particle size within the range from0.1 μm to 50.0 μm, especially within the range from 0.1 μm to 30.0 μm.

The calcium carbonate particles are favorably distinguished by acomparatively low water content. Based on their total weight, they haveexpediently a water content (residual moisture at 200° C.) of not morethan 5.0% by weight, by preference of not more than 2.5% by weight,preferably of not more than 1.0% by weight, particularly preferably ofnot more than 0.5% by weight, yet more preferably less than 0.4% byweight, expediently less than 0.3% by weight, favorably less than 0.2%by weight and in particular within the range from >0.1% by weight to<0.2% by weight.

Within the context of the present invention, the water content of thecalcium salt particles, especially of the calcium carbonate particles,is preferably ascertained by means of thermogravimetry or by means of aninfrared rapid dryer, for example MA35 or MA45 from Sartorius or halogenmoisture analyzer HB43 from Mettler, with the measurement being carriedout preferably under nitrogen (nitrogen flow rate preferably 20 ml/min)and expediently over the temperature range from 40° C. or lower to 250°C. or higher. Furthermore, the measurement is preferably done at aheating rate of 10° C./min.

The specific surface area of the calcium carbonate particles is bypreference less than 3.0 m²/g, preferably less than 2.0 m²/g and inparticular less than 1.5 m²/g. Furthermore, the specific surface area isfavorably greater than 0.25 m²/g, preferably greater than 0.5 m²/g andin particular greater than 0.75 m²/g.

Within the context of a particularly preferred variant of the presentinvention, the calcium carbonate particles, especially the precipitatedcalcium carbonate particles, are preferably sphere-shaped andsubstantially amorphous. Here, the term “amorphous” refers to thosecalcium carbonate forms in which the atoms form at least in part anirregular pattern instead of ordered structures and therefore have onlya short-range order, but not a long-range order. What can bedistinguished therefrom are crystalline forms of the calcium carbonate,such as, for example, calcite, vaterite and aragonite, in whichcrystalline forms the atoms have both a short-range and a long-rangeorder.

Within the context of this preferred variant of the present invention,the presence of crystalline constituents is, however, not categoricallyruled out. By preference, the proportion of crystalline calciumcarbonate is, however, less than 50% by weight, particularly preferablyless than 30% by weight, very particularly preferably less than 15% byweight and in particular less than 10% by weight. Within the context ofa particularly preferred variant of the present invention, theproportion of crystalline calcium carbonate is less than 8.0% by weight,preferably less than 6.0% by weight, expediently less than 4.0% byweight, particularly preferably less than 2.0% by weight, veryparticularly preferably less than 1.0% by weight and in particular lessthan 0.5% by weight, based in each case on the total weight of thecalcium carbonate.

For the ascertainment of the amorphous and the crystalline fractions,X-ray diffraction with an internal standard, preferably quartz, inconjunction with Rietveld refinement has been found to be veryparticularly effective.

Within the context of this preferred embodiment of the presentinvention, the preferably amorphous calcium carbonate particles arefavorably stabilized by at least one substance, especially at least onesurface-active substance, which is preferably arranged on the surface ofthe preferably sphere-shaped calcium carbonate particles. Within thecontext of the present invention, “surface-active substances” referexpediently to organic compounds which strongly build up from theirsolution at interfaces (water/calcium carbonate particles) and therebylower the surface tension, preferably measured at 25° C. For furtherdetails, reference is made to the technical literature, especially toRömpp-Lexikon Chemie [Römpp's Chemistry Lexicon]/editors Jürgen Falbe;Manfred Regitz. revised by Eckard Amelingmeier; Stuttgart, New York;Thieme; volume 2: Cm-G; 10th edition (1997); keyword: “surface-activesubstances”.

By preference, the substance, especially the surface-active substance,has a molar mass greater than 100 g/mol, preferably greater than 125g/mol and in particular greater than 150 g/mol, and satisfies theformula R—X_(n).

In this connection, the radical R represents a radical comprising atleast 1, by preference at least 2, preferably at least 4, particularlypreferably at least 6 and in particular at least 8 carbon atoms, andpreferably represents an aliphatic or cycloaliphatic radical which canoptionally comprise further radicals X and which can optionally have oneor more ether linkages.

The radical X represents a group comprising at least one oxygen atom andat least one carbon atom, sulfur atom, phosphorus atom and/or nitrogenatom, preferably at least one phosphorus atom and/or at least one carbonatom. Particular preference is given to the following groups:

-   -   carboxylic acid groups ˜COOH,    -   carboxylate groups ˜COO⁻,    -   sulfonic acid groups ˜SO₃H,    -   sulfonate groups ˜SO₃ ⁻,    -   hydrogensulfate groups ˜OSO₃H,    -   sulfate groups ˜OSO₃ ⁻,    -   phosphonic acid groups ˜PO₃H₂,    -   phosphonate groups ˜PO₃H⁻, ˜PO₃ ²⁻,    -   amino groups ˜NR¹R² and    -   ammonium groups ˜N⁺R¹R²R³,

especially carboxylic acid groups, carboxylate groups, phosphonic acidgroups and phosphonate groups.

In this context, the radicals R¹, R² and R³ represent, independently ofone another, hydrogen or an alkyl group having 1 to 5 carbon atoms. Oneof the radicals R¹, R² and R³ can also be a radical R.

Preferred counterions for the abovementioned anions are metal cations,especially alkali metal cations, preferably Na⁺ and K⁺, and alsoammonium ions.

Preferred counterions for the abovementioned cations are hydroxyl ions,hydrogencarbonate ions, carbonate ions, hydrogensulfate ions, sulfateions and halide ions, especially chloride ions and bromide ions.

n represents a preferably whole number within the range from 1 to 20,preferably within the range from 1 to 10 and in particular within therange from 1 to 5.

Substances particularly suitable for the purposes of the presentinvention encompass alkylcarboxylic acids, alkyl carboxylates,alkylsulfonic acids, alkyl sulfonates, alkyl sulfates, alkyl ethersulfates having preferably 1 to 4 ethylene glycol ether units, fattyalcohol ethoxylates having preferably 2 to 20 ethylene glycol etherunits, alkylphenol ethoxylates, optionally substituted alkylphosphonicacids, optionally substituted alkyl phosphonates, sorbitan fatty acidesters, alkylpolyglucosides, N-methylglucamides, homopolymers andcopolymers of acrylic acid and also their corresponding salt forms andblock copolymers.

A first group of very particularly advantageous substances areoptionally substituted alkylphosphonic acids, especiallyaminotris(methylenephosphonic acid), 1-hydroxyethylene-(1,1-diphosphonicacid), ethylenediamine tetra(methylenephosphonic acid),hexamethylenediamine tetra(methylenephosphonic acid), diethylenetriaminepenta(methylenephosphonic acid), and optionally substituted alkylphosphonates, especially of the abovementioned acids. These compoundsare known as multifunctional sequestrants for metal ions and scaleinhibitors.

Furthermore, homopolymers and copolymers, preferably homopolymers, ofacrylic acid and their corresponding salt forms have also been found tobe particularly effective, especially those having a weight-averagemolecular weight within the range of 1000 g/mol-10 000 g/mol.

Furthermore, the use of block copolymers, preferably of doublyhydrophilic block copolymers, especially of polyethylene oxide orpolypropylene oxide, is particularly favorable.

The proportion of preferably surface-active substances can be, inprinciple, freely chosen and specifically adjusted for the particularapplication. However, it is preferably within the range from 0.1% byweight to 5.0% by weight, in particular within the range from 0.3% byweight to 1.0% by weight, based on the calcium carbonate content of theparticles.

The preferably sphere-shaped, preferably amorphous calcium carbonateparticles can be produced in a manner known per se, for example byhydrolysis of dialkyl carbonate or of alkylene carbonate in a solutioncomprising calcium cations.

The production of unstabilized, sphere-shaped calcium carbonateparticles is, for example, described in detail in the patent applicationWO 2008/122358, the disclosure of which, especially with regard toparticularly expedient variants of the production of such unstabilized,sphere-shaped calcium carbonate particles, is hereby explicitlyincorporated by reference.

The hydrolysis of the dialkyl carbonate or of the alkylene carbonate isexpediently carried out in the presence of a hydroxide.

Substances which comprise Ca²⁺ ions and are preferred for the purposesof the present invention are calcium halides, preferably CaCl₂, CaBr₂,in particular CaCl₂, and also calcium hydroxide. Within the context of afirst particularly preferred embodiment of the present invention, CaCl₂is used. In a further particularly preferred embodiment of the presentinvention, Ca(OH)₂ is used.

Within the context of a first particularly preferred embodiment of thepresent invention, a dialkyl carbonate is used. Particularly suitabledialkyl carbonates comprise 3 to 20, preferably 3 to 9, carbon atoms,especially dimethyl carbonate, diethyl carbonate, di-n-propyl carbonate,diisopropyl carbonate, di-n-butyl carbonate, di-sec-butyl carbonate anddi-tert-butyl carbonate, with very particular preference being given todimethyl carbonate in this context.

In a further particularly preferred embodiment of the present invention,an alkylene carbonate is reacted. Particularly expedient alkylenecarbonates comprise 3 to 20, preferably 3 to 9, particularly preferably3 to 6, carbon atoms and include especially those compounds comprising aring composed of 3 to 8, preferably 4 to 6, in particular 5, atoms, withpreferably 2 oxygen atoms and otherwise carbon atoms. Propylenecarbonate (4-methyl-1,3-dioxolane) has been found to be veryparticularly effective in this context.

Alkali metal hydroxides, especially NaOH, and calcium hydroxide havebeen found to be particularly suitable as hydroxide. Within the contextof a first particularly preferred embodiment of the present invention,NaOH is used. Within the context of a further particularly preferredembodiment of the present invention, Ca(OH)₂ is used.

Furthermore, the molar ratio of Ca²⁺, preferably of calcium chloride, toOH⁻, preferably alkali metal hydroxide, in the reaction mixture ispreferably greater than 0.5:1 and particularly preferably within therange from >0.5:1 to 1:1, in particular within the range from 0.6:1 to0.9:1.

The molar ratio of Ca²⁺, preferably of calcium chloride, to dialkylcarbonate and/or alkylene carbonate in the reaction mixture is favorablywithin the range from 0.9:1.5 to 1.1:1 and particularly preferablywithin the range from 0.95:1 to 1:0.95. Within the context of a veryparticularly expedient variant of the present invention, the dialkylcarbonate and/or the alkylene carbonate and the Ca²⁺, especially thecalcium chloride, are used equimolarly.

Within the context of a first very particularly preferred variant of thepresent invention, Ca(OH)₂ is not used as OH⁻ source. In thisconnection, the components for the reaction are favorably used in thefollowing concentrations:

-   -   a) Ca²⁺: >10 mmol/L to 50 mmol/L, preferably 15 mmol/L to 45        mmol/L, in particular 17 mmol/L to 35 mmol/L;    -   b) Dialkyl carbonate and/or        -   alkylene carbonate: >10 mmol/L to 50 mmol/L, preferably 15            mmol/L to 45 mmol/L, in particular 17 mmol/L to 35 mmol/L;    -   c) OH⁻: 20 mmol/L to 100 mmol/L, preferably 20 mmol/L to 50        mmol/L, particularly preferably 25 mmol/L to 45 mmol/L, in        particular 28 mmol/L to 35 mmol/L.

In this connection, the respective specified concentrations are based onthe concentrations of the stated components in the reaction mixture.

Within the context of a further very particularly preferred variant ofthe present invention, Ca(OH)₂, preferably lime milk, in particularsaturated lime milk, is used as OH⁻ source. In this connection, thecomponents for the reaction are favorably used in the followingconcentrations:

-   -   a) Ca(OH)₂: >5 mmol/L to 25 mmol/L, preferably 7.5 mmol/L to        22.5 mmol/L, in particular 8.5 mmol/L to 15.5 mmol/L;    -   b) Dialkyl carbonate and/or    -   alkylene carbonate: >5 mmol/L to 25 mmol/L, preferably 7.5        mmol/L to 22.5 mmol/L, in particular 8.5 mmol/L to 15.5 mmol/L.

In this connection, the respective specified concentrations are based onthe concentrations of the stated components in the reaction mixture.

The components are preferably reacted at a temperature within the rangefrom 15° C. to 30° C.

The specific size of the calcium carbonate particles can be controlledin a manner known per se via supersaturation.

The calcium carbonate particles precipitate from the reaction mixtureunder the abovementioned conditions.

The preferably amorphous calcium carbonate particles are expedientlystabilized by addition of the preferably surface-active substance to thereaction mixture.

In this connection, said addition of the substance should take placeonly after the start of the reaction to form the calcium carbonateparticles, i.e., only after addition of the reactants, by preference nosooner than 1 minute, preferably no sooner than 2 minutes, expedientlyno sooner than 3 minutes, particularly preferably no sooner than 4minutes, in particular no sooner than 5 minutes, after mixing of thereactants. Furthermore, the time of addition should be chosen such thatthe preferably surface-active substance is added shortly before the endof the precipitation and as shortly as possible before the start of theconversion of the preferably amorphous calcium carbonate into acrystalline form, since the yield and the purity of the “stabilized,sphere-shaped, amorphous calcium carbonate particles” can be maximizedin this way. If the addition of the preferably surface-active substancetakes place earlier, what is generally obtained is a bimodal productwhich comprises not only the desired, stabilized, sphere-shaped,amorphous calcium carbonate particles, but also ultrafine, amorphouscalcium carbonate particles as secondary product. If the addition of thepreferably surface-active substance takes place later, the conversion ofthe desired “stabilized calcium carbonate particles” into crystallineforms will already start.

For this reason, the preferably surface-active substance is, bypreference, added at a pH less than or equal to 11.5, preferably lessthan or equal to 11.3 and in particular less than or equal to 11.0. Whatis particularly favorable is an addition at a pH within the range from11.5 to 10.0, preferably within the range from 11.3 to 10.5 and inparticular within the range from 11.0 to 10.8, measured in each case atthe reaction temperature, preferably at 25° C.

The resultant, stabilized, preferably sphere-shaped, amorphous calciumcarbonate particles can be dewatered and dried in a manner known per se,for example by centrifugation. It is no longer absolutely necessary towash with acetone and/or to dry in a vacuum drying oven.

By means of drying, “calcium carbonate particles with low structuralwater content” are obtainable from the “stabilized calcium carbonateparticles”.

For the purposes of the present invention, the calcium carbonateparticles obtained are preferably dried such that they have the desiredresidual water content. To this end, what has been found to beparticularly effective is a procedure in which the calcium carbonateparticles are preferably first predried at a temperature up to 150° C.and the calcium carbonate particles are then, by preference, dried at atemperature within the range from greater than 150° C. to 250° C.,preferably within the range from 170° C. to 230° C., particularlypreferably within the range from 180° C. to 220° C. and in particularwithin the range from 190° C. to 210° C. The drying preferably takesplace in a drying oven with air circulation. In said procedure, thecalcium carbonate particles are expediently dried for at least 3 h,particularly preferably for at least 6 h and in particular for at least20 h.

Within the context of a further particularly preferred embodiment of thepresent invention, the proportion of crystalline calcium carbonate, inparticular of calcitic calcium carbonate, is greater than 10% by weight,preferably greater than 25% by weight, favorably greater than 50% byweight, particularly preferably greater than 70% by weight, veryparticularly preferably greater than 80% by weight and in particulargreater than 90% by weight. Furthermore, the proportion of noncalciticcalcium carbonate forms is preferably less than 50% by weight,particularly preferably less than 30% by weight, very particularlypreferably less than 15% by weight and in particular less than 10% byweight. Furthermore, the calcium carbonate particles are as phase-pureas possible. The proportion of peaks of other calcium salts is bypreference less than 5%, preferably less than 2% and in particular lessthan 0.5%. In the best case, peaks of other calcium salt minerals arenot detectable by means of X-ray diffraction.

For the ascertainment of the amorphous and the crystalline fractions andof the phase-purity of the material, X-ray diffraction with an internalstandard, preferably aluminum oxide, in conjunction with Rietveldrefinement has been found to be very particularly effective. Thephase-purity is preferably checked by comparison of a measured and asimulated powder diffractogram.

The basicity of the calcium carbonate particles is comparatively low.Their pH, measured in accordance with EN ISO 787-9, is by preferenceless than 11.5, preferably less than 11.0 and in particular less than10.5.

The sphere-shaped calcium carbonate particles can be produced bycarbonation of an aqueous calcium hydroxide (Ca(OH)₂) suspension. Tothis end, CO₂ or a CO₂-containing gas mixture is expediently conductedinto a calcium hydroxide suspension.

What has been found to be particularly effective is a procedure in which

a. an aqueous calcium hydroxide suspension is initially charged,

b. carbon dioxide or a carbon dioxide-containing gas mixture isintroduced into the suspension from step a. and

c. the resultant calcium carbonate particles are separated off,

with 0.3% by weight to 0.7% by weight, preferably 0.4% by weight to 0.6%by weight and in particular 0.45% by weight to 0.55% by weight of atleast one aminotrisalkylenephosphonic acid being further added.

The concentration of the calcium hydroxide suspension is not subject toany particular restrictions. However, a concentration within the rangefrom 1 g CaO/L to 100 g CaO/L, preferably within the range from 10 gCaO/L to 90 g CaO/L and in particular within the range from 50 g CaO/Lto 80 g CaO/L is particularly favorable.

The aminotrisalkylenephosphonic acid added is preferablyaminotrismethylenephosphonic acid, aminotrisethylenephosphonic acid,aminotrispropylenephosphonic acid and/or aminotrisbutylenephosphonicacid, in particular aminotrismethylenephosphonic acid.

It is possible to control the conversion of the reaction via the amountof CO₂ introduced. However, the carbon dioxide or the carbondioxide-containing gas mixture is preferably introduced until thereaction mixture has a pH less than 9, preferably less than 8 and inparticular less than 7.5.

Furthermore, the carbon dioxide or the carbon dioxide-containing gasmixture is expediently introduced into the calcium hydroxide suspensionat a gas flow rate within the range from 0.02 L CO₂/(h*g Ca(OH)₂) to 2.0L CO₂/(h*g Ca(OH)₂), preferably within the range from 0.04 L CO₂/(h*gCa(OH)₂) to 1.0 L CO₂/(h*g Ca(OH)₂), particularly preferably within therange from 0.08 L CO₂/(h*g Ca(OH)₂) to 0.4 L CO₂/(h*g Ca(OH)₂) and inparticular within the range from 0.12 L CO₂/(h*g Ca(OH)₂) to 0.2 LCO₂/(h*g Ca(OH)₂).

Apart from that, the conversion of the calcium hydroxide suspension withthe carbon dioxide or the carbon dioxide-containing gas mixture takesplace by preference at a temperature less than 25° C., preferably lessthan 20° C. and in particular less than 15° C. On the other hand, thereaction temperature is by preference greater than 0° C., preferablygreater than 5° C. and in particular greater than 7° C.

The addition of the at least one aminotrisalkylenephosphonic acidexpediently takes place during the course of the reaction, preferablyafter an abrupt drop in the conductance of the reaction mixture.Expediently, the at least one aminotrisalkylenephosphonic acid is addedonce the conductivity of the reaction mixture falls by more than 0.5mS/cm/min. In this connection, the decrease in the conductance of thereaction mixture is preferably at least 0.25 mS/cm within 30 seconds, inparticular at least 0.5 mS/cm within 60 seconds. Within the context of aparticularly preferred embodiment of the present invention, the additionof the at least one aminotrisalkylenephosphonic acid takes place at theend of the precipitation of the basic calcium carbonate (BCC;2CaCO₃*Ca(OH)₂*nH₂O).

The calcium carbonate particles precipitate from the reaction mixtureunder the abovementioned conditions and can be separated off and driedin a manner known per se.

Within the context of a preferred embodiment of the present invention,the composite powder according to the invention contains in addition tocalcium carbonate also other calcium salts, preferably calciumphosphates, especially Ca₃(PO₄)₂, CaHPO₄, Ca(H₂PO₄)₂ and/orCa₅(PO₄)₃(OH). In this connection, the weight ratio of calcium carbonateto calcium phosphate is preferably within the range from 99:1 to 1:99and in particular within the range from 50:50 to 99:1.

Within the context of a preferred embodiment of the present invention,the small particles comprise inhibitory calcium carbonate particles. Inthis context, “inhibitory calcium carbonate particles” refer to calciumcarbonate particles which, as additive in polymers, slow down, in thebest case, completely suppress the acid-catalyzed degradation of thepolymer in comparison with the same polymer without additive.

Expediently, the small particles are obtainable by means of a method inwhich calcium carbonate particles are coated with a compositioncomprising, based on its total weight, at least 0.1% by weight of atleast one weak acid.

Within the context of a particularly preferred embodiment of the presentinvention, the inhibitory calcium carbonate is obtainable by means of amethod in which calcium carbonate particles are coated with acomposition comprising, based in each case on its total weight, amixture of at least 0.1% by weight of at least one calcium complexingagent and/or at least one conjugate base, which is an alkali-metal orcalcium salt of a weak acid, together with at least 0.1% by weight of atleast one weak acid.

Within the context of this embodiment, the anions of the calciumcomplexing agent and of the conjugate base can be the same, though thisis not absolutely necessary.

Sodium phosphates, i.e., sodium salts of phosphoric acids, especiallysodium salts of orthophosphoric acid, metaphosphoric acid andpolyphosphoric acid, have been found to be very particularlyadvantageous as calcium complexing agents. Preferred sodium phosphatesencompass sodium orthophosphates, such as primary sodiumdihydrogenphosphate NaH₂PO₄, secondary sodium dihydrogenphosphateNa₂HPO₄ and tertiary trisodium phosphate Na₃PO₄; sodiumisopolyphosphates, such as tetrasodium diphosphate (sodiumpyrophosphate) Na₄P₂O₇, pentasodium triphosphate (sodiumtripolyphosphate) Na₅P₃O₁₀; and higher-molecular-weight sodiumphosphates, such as sodium metaphosphates and sodium polyphosphates,such as fused or calcined phosphates, Graham's salt (approximatecomposition Na₂O*P₂O₅, sometimes also referred to as sodiumhexametaphosphate), Kurrol's salt and Maddrell's salt. According to theinvention, very particular preference is given to using sodiumhexametaphosphate. The use of the abovementioned phosphates isparticularly advantageous especially in a composite powder for implants,since the phosphates additionally promote bone formation in this case.

Further suitable calcium complexing agents include joint polydentate,chelating ligands, especially ethylenediaminetetraacetic acid (EDTA),triethylenetetramine, diethylenetriamine, o-phenanthroline, oxalic acidand mixtures thereof.

Weak acids particularly suitable for the purposes of the presentinvention have a pK_(a), measured at 25° C., greater than 1.0,preferably greater than 1.5 and in particular greater than 2.0. At thesame time, the pK_(a) of suitable weak acids, measured at 25° C., is bypreference less than 20.0, preferably less than 10.0, particularlypreferably less than 5.0, expediently less than 4.0 and in particularless than 3.0. Weak acids very particularly suitable according to theinvention encompass phosphoric acid, metaphosphoric acid,hexametaphosphoric acid, citric acid, boric acid, sulfurous acid, aceticacid and mixtures thereof. Phosphoric acid is very particularlypreferably used as weak acid.

Conjugate bases preferred according to the invention include especiallysodium or calcium salts of the abovementioned weak acids, with veryparticular preference being given to sodium hexametaphosphate.

The inhibitory calcium carbonate particles can be produced in a mannerknown per se by coating calcium carbonate particles with a compositioncomprising at least one weak acid.

Particularly preferably, the inhibitory calcium carbonate particles areproduced in a manner known per se by coating calcium carbonate particleswith a composition comprising at least one calcium complexing agentand/or at least one conjugate base, which is an alkali-metal or calciumsalt of a weak acid, together with at least one weak acid. Thesimultaneous coating with at least one calcium complexing agent and/orat least one conjugate base, which is an alkali-metal or calcium salt ofa weak acid, together with at least one weak acid leads to particularlypreferred calcium carbonate particles.

Expediently, what is initially charged is an aqueous suspension of thecalcium carbonate particles to be coated, which, based on its totalweight, favorably has a content of calcium carbonate particles withinthe range from 1.0% by weight to 80.0% by weight, preferably within therange from 5.0% by weight to 50.0% by weight and in particular withinthe range from 10.0% by weight to 25.0% by weight.

The calcium carbonate particles are favorably coated by addition of thestated substance or substances in pure form or in aqueous solution, withaqueous solutions of the stated component or components having beenfound to be very particularly advantageous according to the inventionfor achieving a coating of the calcium carbonate particles which is ashomogeneous as possible.

Furthermore, it is particularly favorable within the context of thepresent invention to add the calcium complexing agent and/or theconjugate base, which is an alkali-metal or calcium salt of a weak acid,before the weak acid.

The calcium complexing agent or the conjugate base is used by preferencein an amount within the range from 0.1 part by weight to 25.0 parts byweight, preferably within the range from 0.5 part by weight to 10.0parts by weight and in particular within the range from 1.0 part byweight to 5.0 parts by weight, based in each case on 100 parts by weightof the calcium carbonate particles to be coated. In this connection, theamount of the calcium complexing agent or of the conjugate base isexpediently chosen such that a complete coating of the surface of thecalcium carbonate particles with the calcium complexing agent theconjugate base is achieved.

The weak acid is used by preference in an amount within the range from0.1 part by weight to 30.0 parts by weight, preferably within the rangefrom 0.5 part by weight to 15.0 parts by weight, particularly preferablywithin the range from 1.0 part by weight to 10.0 parts by weight and inparticular within the range from 4.0 parts by weight to 8.0 parts byweight, based in each case on 100 parts by weight of the calciumcarbonate particles to be coated.

The inhibitory calcium carbonate particles obtainable in this way arestable in a moderately acidic environment, this capability beingattributed to a buffer effect due to the weak acid, preferably due tothe absorbed or reacted calcium complexing agent or the conjugate baseon the surface of the calcium carbonate particles and the weak acid,with especially the application of the calcium complexing agent and/orof the conjugate base on the surface of the calcium carbonate particleslowering in turn the solubility of the surface of the calcium carbonateparticles and thus stabilizing the calcium carbonate particles, withoutit being intended that the teaching of the present invention be tied tothis theory.

The composite powder is, according to the invention, obtainable by meansof a method in which large particles are combined with small particles,wherein

-   -   the large particles have an average particle diameter within the        range from 0.1 μm to 10 mm, preferably within the range from 5        μm to 10 mm, particularly preferably within the range from 10 μm        to 10 mm, favorably within the range from 20 μm to 10 mm,        advantageously within the range from 30 μm to 2.0 mm and in        particular within the range from 60.0 μm to 500.0 μm,    -   the average particle diameter of the small particles is by        preference not more than ⅕, preferably not more than 1/10,        particularly preferably not more than 1/20 and in particular not        more than 1/1000 of the average particle diameter of the large        particles.

In this connection, the small particles are arranged on the surface ofthe large particles and/or distributed inhomogeneously within the largeparticles. Within the context of a particularly preferred embodiment ofthe present invention, especially for resorbable polymers and forUHMWPE, excellent results are achieved, however, when the smallparticles are arranged at least in part on the surface of the largeparticles and preferably cover them incompletely. Very particularlypreferably, the small particles are arranged on the surface of the largeparticles and preferably cover them incompletely.

Here, an “inhomogeneous” distribution of the small particles orfragments thereof within the large particles means a distribution of thesmall particles or fragments thereof within the large particles that isnot homogeneous (uniform). Preferably, there are, within the particlesof the composite powder, at least one first region that comprises atleast two, by preference at least three, preferably at least four and inparticular at least five small particles or fragments thereof and atleast one other region within the particles of the composite powder thathas the same volume and the same shape as the first region, butcomprises a different number of small particles.

Within the context of a preferred embodiment of the present invention,the weight ratio of polymer, especially polyamide, to precipitatedcalcium carbonate in the particle interior is greater than the weightratio of polymer, especially polyamide, to precipitated calciumcarbonate in the exterior of the particles. Expediently, the weightratio of polymer, especially polyamide, to precipitated calciumcarbonate in the particle interior is greater than 50:50, preferablygreater than 60:40, favorably greater than 70:30, particularlypreferably greater than 80:20, yet more preferably greater than 90:10,very particularly preferably greater than 95:5 and in particular greaterthan 99:1. Furthermore, the weight ratio of precipitated calciumcarbonate to polymer, especially polyamide, in the exterior of theparticles, preferably in the preferential exterior of the particles, isgreater than 50:50, preferably greater than 60:40, favorably greaterthan 70:30, particularly preferably greater than 80:20, yet morepreferably greater than 90:10, very particularly preferably greater than95:5 and in particular greater than 99:1.

Within the context of a further preferred embodiment of the presentinvention, the small particles are arranged on the surface of the largeparticles and preferably cover the large particles incompletely.Expediently, at least 0.1%, preferably at least 5.0% and in particular50.0% of the surface of the large particles are not coated with thesphere-shaped calcium carbonate particles. Preferably, this effect isenhanced by the gaps between individual calcium carbonate particles,which are preferably present and lead to the formation of correspondingmicrochannels for fluidic substances, especially for a polymer melt ofthe large particles. This structure is especially advantageous for usesof the composite powder in laser sintering methods, since this ensures auniform and rapid melting of the polymer present in the compositepowder, preferably the thermoplastic polymer, particularly preferablythe resorbable polymer, in particular the lactic acid polymer.

Within the context of a particularly preferred embodiment of the presentinvention, the composite powder according to the invention ischaracterized by a specific particle-size distribution. Firstly, theparticles of the composite powder have, by preference, an averageparticle size d₅₀ within the range from 10 μm to less than 200 μm,preferably within the range from 20 μm to less than 200 μm, particularlypreferably within the range from 20 μm to less than 150 μm, favorablywithin the range from 20 μm to less than 100 μm and in particular withinthe range from 35 μm to less than 70 μm.

Furthermore, fine-particle proportion of the composite powder is bypreference less than 50.0% by volume, preferably less than 45.0% byvolume, particularly preferably less than 40.0% by volume, yet morepreferably less than 20.0% by volume, favorably less than 15.0% byvolume, expediently less than 10.0% by volume and in particular lessthan 5.0% by volume. In this connection, the fine-particle proportionrefers to, according to the invention, the proportion of the smallestparticle population in the case of a bimodal or multimodal particle-sizedistribution, based on the total amount for the cumulative distributioncurve. In the case of a unimodal (monodisperse) particle-sizedistribution, the fine-particle proportion is, according to theinvention, defined as 0.0% by volume. In this context, what are takeninto consideration are all particles present in the product, includingnoncombined starting material, especially small particles within thecontext of the invention as well as fragments of the large and/or thesmall particles within the context of the invention.

For composite powder having an average particle size d₅₀ within therange from greater than 40 μm to less than 200 μm, the fine-particleproportion is preferably such that the proportion of particles in theproduct having a particle size less than 20 μm is by preference lessthan 50.0% by volume, preferably less than 45.0% by volume, particularlypreferably less than 40.0% by volume, yet more preferably less than20.0% by volume, favorably less than 15.0% by volume, expediently lessthan 10.0% by volume and in particular less than 5.0% by volume, with“particles” in this context encompassing especially particles of thecomposite powder within the context of the invention, small particleswithin the context of the invention and fragments of the large and/orthe small particles within the context of the invention, provided thatthey have the stated particle size.

For composite powder having an average particle size d₅₀ within therange from 10 μm to 40 μm, the fine-particle proportion is preferablysuch that the proportion of particles in the product having a particlesize less than 5 μm is by preference less than 50.0% by volume,preferably less than 45.0% by volume, particularly preferably less than40.0% by volume, yet more preferably less than 20.0% by volume,favorably less than 15.0% by volume, expediently less than 10.0% byvolume and in particular less than 5.0% by volume, with “particles” inthis context encompassing especially particles of the composite powderwithin the context of the invention, small particles within the contextof the invention and fragments of the large and/or the small particleswithin the context of the invention, provided that they have the statedparticle size.

Furthermore, the density of the fine-particle proportion is bypreference less than 2.6 g/cm³, preferably less than 2.5 g/cm³,particularly preferably less than 2.4 g/cm³ and in particular within therange from greater than 1.2 g/cm³ to less than 2.4 g/cm³, with thisvalue preferably being determined by separating off the fine-particleproportion by means of sieving and by measuring the density of thefraction separated off.

Preferably, the particles of the composite powder have a particle sized₉₀ of less than 350 μm, by preference less than 300 μm, preferably lessthan 250 μm, particularly preferably less than 200 μm and in particularless than 150 μm. Furthermore, the particle size d₉₀ is by preferencegreater than 50 μm, preferably greater than 75 μm and in particulargreater than 100 μm.

Expediently, the ratio d₂₀/d₅₀ is less than 100%, by preference lessthan 75%, preferably less than 65%, particularly preferably less than60% and in particular less than 55%. Furthermore, the ratio d₂₀/d₅₀ isexpediently greater than 10%, by preference greater than 20%, preferablygreater than 30%, particularly preferably greater than 40% and inparticular greater than 50%.

Within the context of the present invention, the abovementionedvariables d₂₀, d₅₀ and d₉₀ are defined as follows:

d₂₀ refers to the particle size of the particle-size distribution, atwhich 20% of the particles have a particle size less than the specifiedvalue and 80% of the particles have a particle size greater than orequal to the specified value.

d₅₀ refers to the average particle size of the particle-sizedistribution. 50% of the particles have a particle size less than thespecified value and 50% of the particles have a particle size greaterthan or equal to the specified value.

d₉₀ refers to the particle size of the particle-size distribution, atwhich 90% of the particles have a particle size less than the specifiedvalue and 10% of the particles have a particle size greater than orequal to the specified value.

The particle-size distribution of this embodiment can be achieved in amanner known per se by classification of the composite powder, i.e., byseparation of a disperse solids mixture into fractions. Preferably,classification is done according to particle size or particle density.Dry sieving, wet sieving and air-jet sieving, especially air-jetsieving, as well as flow classification, especially by means of airclassification, are particularly advantageous.

Within the context of a particularly preferred embodiment of the presentinvention, the composite powder is classified in a first step formaximum removal of the coarse fraction greater than 800 μm, preferablygreater than 500 μm and in particular greater than 250 μm. In thiscontext, what has been found to be particularly effective is dry sievingover a coarse sieve which has, by preference, a size within the rangefrom 250 μm to 800 μm, preferably within the range from 250 μm to 500 μmand in particular of 250 μm, with size meaning the size of the openings.

In a further step, the composite powder is preferably classified formaximal removal of the fine fraction <20 μm. In this context, air-jetsieving and air classification have been found to be particularlyfavorable.

According to the invention, the average diameter of the particles of thecomposite powder, of the large particles and of the small particles, theparticle sizes d₂₀, d₅₀, d₉₀ and also the abovementioned longitudinalsizes are expediently ascertained on the basis of micrographs, possiblyon the basis of electron micrographs. For the ascertainment of theaverage diameter of the large particles and of the small particles andalso of the particles of the composite powder and for the particle sizesd₂₀, d₅₀, d₉₀, sedimentation analyses are also particularlyadvantageous, with the use of a Sedigraph 5100 (Micromeritics GmbH)being particularly favorable here. For the particles of the compositepowder, particle-size analyses with laser diffraction have also beenfound to be particularly effective, with the use of a HELOS/F laserdiffraction sensor from Sympatec GmbH being particularly advantageous inthis context. It preferably comprises a RODOS dry disperser.

Apart from that, these data and also all other data in the presentdescription are, unless otherwise specified, based on a temperature of23° C.

The composite powder according to the invention is comparativelycompact. By preference, the proportion of subregions inside theparticles of the composite powder that have a density less than 0.5g/cm³ and in particular less than 0.25 g/cm³ is less than 10.0%,preferably less than 5.0% and in particular less than 1.0%, based ineach case on the total volume of the composite powder.

The proportion by weight of the sphere-shaped calcium carbonateparticles, based on the total weight of the composite powder, is bypreference at least 0.1% by weight, preferably at least 1.0% by weightand particularly preferably at least 5.0% by weight and is expedientlywithin the range from 5.0% by weight to 80.0% by weight, particularlypreferably within the range from 10.0% by weight to 60.0% by weight andfavorably within the range from 20.0% by weight to 50.0% by weight. Forsphere-shaped calcium carbonate particles, which, based on the totalamount of sphere-shaped calcium carbonate particles, contain more than15.0% by weight of particles of a size less than 20 μm and/or particlesof a size greater than 250 μm, what has been found to be veryparticularly effective is a total amount of sphere-shaped calciumcarbonate particles within the range from 35.0% by weight to 45.0% byweight. For sphere-shaped calcium carbonate particles, which, based onthe total amount of sphere-shaped calcium carbonate particles, containnot more than 15.0% by weight of particles of a size less than 20 μmand/or particles of a size greater than 250 μm, what has been found tobe very particularly effective is a total amount of sphere-shapedcalcium carbonate particles within the range from 20.0% by weight to30.0% by weight.

The proportion by weight of the polymer and preferably of thethermoplastic polymer, based on the total weight of the compositepowder, is by preference at least 0.1% by weight, preferably at least1.0% by weight and particularly preferably at least 5.0% by weight andis expediently within the range from 20.0% by weight to 95.0% by weight,preferably within the range from 40.0% by weight to 90.0% by weight andfavorably within the range from 50.0% by weight to 80.0% by weight.

For a composite powder containing sphere-shaped calcium carbonateparticles, which, based on the total amount of sphere-shaped calciumcarbonate particles, contain more than 20.0% by weight of particles of asize less than 20 μm and/or particles of a size greater than 250 μm,what has been found to be very particularly effective is a total amountof polymer within the range from 55.0% by weight to 65.0% by weight. Fora composite powder containing sphere-shaped calcium carbonate particles,which, based on the total amount of sphere-shaped calcium carbonateparticles, contain not more than 20.0% by weight of particles of a sizeless than 20 μm and/or particles of a size greater than 250 μm, what hasbeen found to be very particularly effective is a total amount ofpolymer within the range from 70.0% by weight to 80.0% by weight.

The composite powder is distinguished by, inter alia, a very goodcombination of the first material with the second material. The firmcombination of the first material with the second material canpreferably be verified by subjecting the composite powder to mechanicalstress, especially by shake extraction of the composite powder withnonsolvent for the polymer and sphere-shaped calcium carbonate at 25°C., preferably in accordance with the procedure described in Organikum,17th edition, VEB Deutscher Verlag der Wissenschaften, Berlin, 1988,section 2.5.2.1 “Ausschütteln von Lösungen bzw. Suspensionen” [shakeextraction of solutions or suspensions], pages 56-57. The shake time isby preference at least one minute, preferably at least 5 minutes and inparticular 10 minutes, and preferably does not lead to a substantialchange in the shape, the size and/or the composition of the particles ofthe composite powder. Particularly preferably, there is no change afterthe shake test for at least 60% by weight, by preference at least 70% byweight, preferably at least 80% by weight, particularly preferably atleast 90% by weight, favorably at least 95% by weight and in particularat least 99% by weight of the particles of the composite powder, withrespect to their composition, their size and preferably their shape. Anonsolvent which is particularly suitable in this context is water,especially for polyamide-containing composite powder.

Furthermore, the particles of the composite powder according to theinvention usually have a comparatively isotropic particle shape, whichis especially advantageous for uses of the composite powder in SLMmethods. The normally virtually sphere-shaped particle shape of theparticles of the composite powder generally leads to an avoidance or atleast to a reduction of negative influences, such as warpage orshrinkage. Consequently, a very advantageous melting and solidificationbehavior of the composite powder can usually also be observed.

In contrast, conventional powder particles, which are obtained bycryogenic grinding for example, have an irregular (amorphous) particleshape with sharp edges and pointed corners. However, such powders arenot advantageous for SLM methods because of their disadvantageousparticle shape and additionally because of their comparatively wideparticle-size distribution and because of their comparatively high finefraction of particles <20 μm.

By means of the calcium carbonate particles and especially by means ofthe precipitated calcium carbonate particles, it is possible tospecifically influence and control the properties of the polymer,especially of the thermoplastic polymer. For instance, the calciumcarbonate particles and especially the precipitated calcium carbonateparticles allow a very good buffering and pH stabilization of thepolymer, especially of the thermoplastic polymer. Furthermore, thebiocompatibility of the polymer, especially of the thermoplasticpolymer, is distinctly improved by the calcium carbonate particles andespecially by the precipitated calcium carbonate particles. Furthermore,a distinct suppression of the thermal degradation of the polymer,especially of the thermoplastic polymer, is observed when using theinhibitory calcium carbonate particles.

The composite powder according to the invention can be produced in amanner known per se, for example by means of a one-step method,especially by surface precipitation or coating, preferably by coatingwith grinding material. Furthermore, what is also particularly suitableis a procedure in which polymer particles are precipitated from apolymer solution which additionally contains small particles within thecontext of the invention, preferably in suspended form.

However, what has been found to be particularly effective is a procedurein which polymer particles and sphere-shaped calcium carbonate particlesare contacted with one another and are combined with one another by theaction of mechanical forces. Expediently, this is done in a suitablemixer or in a mill, especially in an impact mill, pin mill or in anultrarotor mill. In this connection, the rotor speed is by preferencegreater than 1 m/s, preferably greater than 10 m/s, particularlypreferably greater than 25 m/s and in particular within the range from50 m/s to 100 m/s.

The temperature at which the composite powder is produced canfundamentally be freely chosen. However, temperatures greater than −200°C., by preference greater than −100° C., preferably greater than −50°C., particularly preferably greater than −20° C. and in particulargreater than 0° C. are particularly advantageous. On the other hand, thetemperature is advantageously less than 120° C., by preference less than100° C., preferably less than 70° C., particularly preferably less than50° C. and in particular less than 40° C. Temperatures within the rangefrom greater than 0° C. to less than 50° C. and in particular within therange from greater than 5° C. to less than 40° C. have been found to bevery particularly effective.

Within the context of a particularly preferred embodiment of the presentinvention, the mixer or the mill, especially the impact mill, the pinmill or the ultrarotor mill, is cooled during the production of thecomposite powder according to the invention in order to dissipate theenergy which is released. By preference, cooling is achieved with acoolant having a temperature less than 25° C., preferably within therange from less than 25° C. to −60° C., particularly preferably withinthe range from less than 20° C. to −40° C., expediently within the rangefrom less than 20° C. to −20° C. and in particular within the range fromless than 15° C. to 0° C. Furthermore, the cooling is preferablydimensioned such that, at the end of the mixing or grinding operation,preferably the grinding operation, the temperature in the mixing orgrinding space, preferably in the grinding space, is less than 120° C.,by preference less than 100° C., preferably less than 70° C.particularly preferably less than 50° C. and in particular less than 40°C.

According to a particularly preferred embodiment of the presentinvention, this procedure leads, especially in the case of polyamides,to the sphere-shaped calcium carbonate particles penetrating into theinterior of the polymer particles and being covered by the polymer ascompletely as possible, with the result that they are not identifiablefrom the outside. Such particles can be processed and used like thepolymer without the sphere-shaped calcium carbonate particles, but havethe improved properties of the composite powder according to theinvention.

Within the context of a first particularly preferred variant of thepresent invention, the composite powder is produced following theprocedure described in the patent application JP62083029 A. In thisprocedure, a first material (so-called mother particles) is coated onthe surface with a second material consisting of smaller particles(so-called baby particles). For this purpose, preference is given tousing a surface-modification device (“hybridizer”) which comprises ahigh-speed rotor, a stator and a sphere-shaped vessel, preferablycomprising internal blades. The use of NARA hybridization systems, whichpreferably have an outer rotor diameter of 118 mm, especially of ahybridization system with the designation NHS-0 or NHS-1 from NARAMachinery Co., Ltd., has been found to be particularly effective in thiscontext.

The mother particles and the baby particles are mixed, preferably finelydistributed and introduced into the hybridizer. There the mixture ispreferably further finely distributed and preferably repeatedly exposedto mechanical forces, especially impact forces, compression forces,friction forces and shear forces as well as the mutual interactions ofthe particles, in order to embed the baby particles in the motherparticles in a uniform manner.

Preferred rotor speeds are within the range from 50 m/s to 100 m/s,based on the circumferential speed.

For further details in relation to this method, especially with regardto the particularly expedient embodiments, reference is made toJP62083029 A, the disclosure of which, including the particularlyexpedient method variants, is explicitly incorporated into the presentapplication by reference.

Within the context of a further particularly preferred variant of thepresent invention, the composite powder is produced following theprocedure described in the patent application DE 42 44 254 A1.Accordingly, a method for producing a composite powder by attaching asubstance on the surface of a thermoplastic material is particularlyfavorable when the thermoplastic material has an average particlediameter of from 100 μm to 10 mm and the substance has a smallerparticle diameter and a better heat resistance than the thermoplasticmaterial, especially when the method comprises the steps of:

-   -   first heating the substance which has the smaller particle        diameter and the better heat resistance than the thermoplastic        material to a temperature which is preferably not less than the        softening point of the thermoplastic material, while stirring in        a device which preferably has a stirrer and a heater;    -   adding the thermoplastic material into the device; and    -   attaching the substance having the better heat resistance on the        surface of the thermoplastic material.

For further details in relation to this method, especially with regardto the particularly expedient embodiments, reference is made to DE 42 44254 A1, the disclosure of which, including the particularly expedientmethod variants, is explicitly incorporated into the present applicationby reference.

Within the context of yet a further particularly preferred variant ofthe present invention, the composite powder is produced following theprocedure described in the patent application EP 0 922 488 A1 and/or inthe U.S. Pat. No. 6,403,219 B1. Accordingly, what is particularlyadvantageous is a method for producing a composite powder by attachingor adhesively mounting fine particles on the surface of a solid particlewhich acts as a core, by application of an impact and subsequent growthof one or more crystals on the core surface.

For further details in relation to this method, especially with regardto the particularly expedient embodiments, reference is made to thepatent application EP 0 922 488 A1 and/or the U.S. Pat. No. 6,403,219B1, the disclosures of which, including the particularly expedientmethod variants, are explicitly incorporated into the presentapplication by reference.

Within the context of a further particularly preferred embodiment of thepresent invention, the composite powder is subjected to a fixingoperation following the procedure described in the patent application EP0 523 372 A1. This procedure is especially expedient for a compositepowder which were obtained following the method described in the patentapplication JP62083029 A. In this connection, the particles of thecomposite powder are preferably fixed by means of thermal plasmaspraying, with preference being given to using a reduced-pressure plasmaspraying device which preferably has an output of at least 30 kW,especially the instrument described in EP 0 523 372 A1.

For further details in relation to this method, especially with regardto the particularly expedient embodiments, reference is made to thepatent application EP 0 523 372 A1, the disclosure of which, includingthe particularly expedient method variants, is explicitly incorporatedinto the present application by reference.

The composite powder according to the invention is distinguished by anexcellent property profile which suggests its use especially in lasersintering methods. Its excellent pourability and its excellentflowability allow, in the case of laser sintering, the production ofcomponents having excellent surface quality and surface nature as wellas improved component density. At the same time, the composite powderaccording to the invention exhibits a very good shrinkage behavior andan excellent dimensional stability. Furthermore, a betterheat-conductivity behavior outside the laser-treated region can beestablished.

Furthermore, the composite powder according to the invention has acomparatively high isotropy, which allows an extremely uniform meltingof the composite powder. This behavior can be utilized in SLM methodsfor the production of components having high quality, high componentdensity, low porosity and low number of imperfections.

Furthermore, the presence of the sphere-shaped calcium carbonateparticles in the composite powder allows an excellent pH stabilization(buffering) in later applications, especially in those polymers whichcontain acid groups or can release acids under certain conditions. Theseinclude, for example, polyvinyl chloride and polylactic acid.

Furthermore, any other, more expensive materials can be replaced withthe composite powder according to the invention in order to thus achievea price reduction of the end product.

According to the invention, the properties of the composite powder,especially its flowability, can also be controlled and, if needed,specifically adjusted via the moistness of the composite powder. On theone hand, the flowability of the composite powder fundamentallyincreases with increasing moistness, which facilitates theprocessability of the composite powder. On the other hand, a highermoistness of the composite powder can, especially in the case of thermalprocessing of the composite powder, particularly in the presence ofimpurities and/or the presence of very fine particles, lead to thermaldegradation or hydrolysis of the polymer and to process disturbances.

Against this background, the moistness of the composite powder accordingto the invention is by preference less than 2.5% by weight, preferablyless than 1.5% by weight, particularly preferably less than 1.0% byweight, yet more preferably less than 0.9% by weight, favorably lessthan 0.8% by weight, expediently less than 0.6% by weight, veryparticularly preferably less than 0.5% by weight and in particular lessthan 0.25% by weight. On the other hand, the moistness of the compositepowder according to the invention is by preference greater than 0.000%by weight, preferably greater than 0.010% by weight and in particulargreater than 0.025% by weight.

In this context, the use of the inhibitory calcium carbonate allows anagain improved thermal processability of the composition. The processingwindow (temperature window) is distinctly greater than with conventionalcalcium carbonate and a thermal degradation or a hydrolysis of a polymeris again significantly suppressed.

The desired moistness of the composite powder can be achieved byinherently known predrying of the composite powder prior to processing,with drying in the production process being fundamentally advisable. Fora stable process management, what has been found to be very particularlyfavorable in this context is drying up to a moisture content within therange from 0.01% by weight to 0.1% by weight. Furthermore, the use of amicrowave vacuum dryer has been found to very particularly effective.

The further processing of the composite powder can be done comparativelyeasily, since, according to the solution according to the invention,only one component (the composite powder) and no longer two components(sphere-shaped calcium carbonate particles and polymer) are to beprocessed. Dispersion problems are not noticeable owing to the firmcombination between the polymer and the sphere-shaped calcium carbonateparticles.

Furthermore, it is possible, via the choice of the proportions and ofthe size of the particular individual components, to specificallycontrol the microstructure, the melting behavior and the flow behaviorof the composite powder. These properties of the composite powder can inturn be utilized in order to specifically control the end structure ofthe resultant components, especially their biological compatibility,their biodegradability and their mechanical properties.

It is generally not necessary to add further processing aids, especiallyspecific solvents, when processing the composite powder. This extendsthe possible application areas of the composite powder especially in thepharmaceutical sector and in the food sector.

The composite powder can be directly used as such. Owing to itsexcellent property profile, the composite powder is, however, especiallysuitable as additive, particularly preferably as polymer additive, asadditive substance or starting material for compounding, for theproduction of components, for applications in medical technology and/orin microtechnology and/or for the production of foamed articles.Particularly preferred medical technology applications preferablyinclude resorbable implants. Particularly expedient application areasencompass injection-molded screws, pressed plates, especiallymelt-pressed plates, foamed implants and pourable powders for selectivemanufacturing methods, and, in the last case, the overall particle sizeof the particles of the composite powder is preferably less than 3 mmand preferably greater than 5.0 μm.

As polymer additive, the composite powder is preferably added to atleast one polymer, especially one thermoplastic polymer, as matrixpolymer. Here, particular preference is given to the polymers which canalso be used as component of the composite powder. To avoid repetition,reference is therefore made to the above remarks, especially withrespect to the preferred forms of the polymer. Very particularlypreferred matrix polymers include polyvinyl chloride (PVC), polyurethane(PU), silicone, polypropylene (PP), polyethylene (PE), especiallyUHMWPE, and polylactic acid (PLA).

Within the context of the present invention, the matrix polymer and thepolymer of the composite powder are preferably miscible with one anotherat the application temperature, particularly preferably chemicallyidentical.

Particularly preferred compositions contain 40.0% by weight to 99.9% byweight of at least one matrix polymer and 0.1% by weight to 50.0% byweight of at least one composite powder according to the invention.

The composition can be produced in a manner known per se by mixing thecomponents.

The composition can then be further processed in a customary manner, inparticular granulated, ground, extruded, injection-molded, foamed orelse used in 3D-printing methods.

Furthermore, the composite powder can be further processed and/or useddirectly, i.e., without addition of additional polymers.

The advantages of the composite powder are, in this connection,noticeable especially when granulating, grinding, extruding,injection-molding, melt-pressing, foaming and/or 3D-printing thecomposite powder.

Within the context of the present invention, polymer foams arepreferably produced by the generation or introduction of a gaseous phaseinto a composition comprising the composite powder and possibly at leastone matrix polymer. In this case, the goal is to distribute the gas inthe composition as uniformly as possible in order to achieve a uniformand homogeneous foam structure. The gas can be introduced in differentways.

Preferably, the gas phase is generated by addition of a blowing agent.Blowing agents refer to substances which release gases as a result ofchemical reactions (chemical blowing agents) or as a result of phasetransition (physical blowing agents). In the case of foam extrusion orin the case of foam injection-molding, the chemical blowing agent isadmixed in the mold of a master batch of the composition or physicalblowing agent is directly injected under pressure into the melt of thecomposition. The injection is referred to as direct gas-injection and isused especially when processing thermoplastic polymers.

Furthermore, the composite powder according to the invention isespecially suitable for the production of implants which can replaceconventional metal implants for bone fractures. The implants serve tofix the bones until the fracture is healed. Whereas metal implantsnormally remain in the body or must be removed in a further operation,the implants obtainable from the composite powder according to theinvention act as a temporary aid. They expediently comprise polymerswhich the body itself can degrade and substances which supply calciumand preferably valuable phosphorus substances for bone formation. Theadvantages which arise for the patient are clear: no further operationfor the removal of the implant and a quickened bone regeneration.

According to a particularly preferred variant of the present invention,the composite powder according to the invention is used for theproduction of components, especially implants, by means of selectivelaser sintering. Expediently, a bed of powder of tightly packedparticles of the composite powder according to the invention is easilypartially or fully melted locally (just the polymer) with the aid of alaser scanner unit, a directly deflected electron beam or an infraredheater with a geometry-representing mask. The particles solidify owingto cooling as a result of heat transfer and thus combine to form a solidlayer. The powder particles which are not partially melted remain assupport material in the component and are preferably removed after theconstruction process has ended. By means of renewed coating with powder,it is possible, in analogy with the first layer, for further layers tobe hardened and to be combined with the first layer.

Laser types particularly suitable for laser sintering methods are allthe ones which cause the polymer of the composite powder according tothe invention to sinter, to fuse or to crosslink, in particular CO2laser (10 μm) ND-YAG laser (1060 nm), He—Ne laser (633 nm) or dye laser(350-1000 nm). Preference is given to using a CO2 laser.

In the case of the irradiation, the energy density in the packed bed is,by preference, from 0.1 J/mm³ to 10 J/mm³.

Depending on the application, the effective diameter of the laser beamis, by preference, from 0.01 nm to 0.5 nm, preferably 0.1 nm to 0.5 nm.

Preference is given to using pulsed lasers, with a high pulse frequency,especially from 1 kHz to 100 kHz, having been found to be particularlysuitable.

The preferred procedure can be described as follows: The laser beamstrikes the top layer of the packed bed composed of the material to beused according to the invention and, while doing so, sinters thematerial within a certain layer thickness. Said layer thickness can befrom 0.01 mm to 1 mm, preferably from 0.05 mm to 0.5 mm. The first layerof the desired component is generated in this way. Thereafter, theworking space is lowered by an amount which is lower than the thicknessof the layer sintered together. The working space is filled up to theoriginal level with additional polymer material. By means of renewedirradiation with the laser, the second layer of the component issintered and combined with the previous layer. By repeating theoperation, the further layers are generated until the component iscompleted.

The exposure rate in the case of the scanning of the laser is preferably1 mm/s to 1000 mm/s. Typically, a rate of about 100 mm/s is used.

In the present case, what has been found to be particularly effectivefor the partial or full melting of the polymer is heating to atemperature within the range from 60° C. to 250° C., preferably withinthe range from 100° C. to 230° C. and in particular within the rangefrom 150° C. to 200° C.

The present invention also provides components obtainable by selectivelaser sintering of a composition comprising a composite powder accordingto the invention, with implants for uses in the field of neurosurgery,oral surgery, jaw surgery, facial surgery, neck surgery, nose surgeryand ear surgery as well as hand surgery, foot surgery, thorax surgery,rib surgery and shoulder surgery being excluded as components.

The proportion by weight of the composite powder according to theinvention in the composition is by preference at least 50.0% by weight,preferably at least 75.0% by weight, particularly preferably at least90.0% by weight and in particular at least 99.0% by weight. Within thecontext of a very particularly embodiment of the present invention, thecomposition contains only the composite powder according to theinvention.

The components according to the invention are favorably distinguished bythe following properties:

-   -   excellent surface quality,    -   excellent surface nature,    -   excellent component density, preferably greater than 95%, in        particular greater than 97%,    -   excellent shrinkage behavior,    -   excellent dimensional stability,    -   very few imperfections,    -   very relatively low porosity,    -   very low content of degradation products,    -   excellent three-point bending strength, preferably greater than        60 MPa, particularly preferably greater than 65 MPa, in        particular greater than 70 MPa,    -   excellent elastic modulus, preferably 3420 N/mm², particularly        preferably greater than 3750 N/mm², favorably greater than 4000        N/mm², in particular greater than 4500 N/mm²,    -   excellent pH stability,    -   excellent biological compatibility,    -   excellent biocompatibility,    -   excellent osteoconduction,    -   excellent resorbability,    -   excellent biodegradability.

A thermoplastic further processing of the composite particles accordingto the invention usually brings about an at least partial fusion of thecomposite particles as a result of the partial or full melting of thepolymer present therein. Preferably, said thermoplastic furtherprocessing does not lead, however, to a homogeneous distribution of thesmall particles or fragments thereof on the surface or in the interiorof the now fused polymer, especially since the calcium carbonateparticles preferably do not partially or fully melt under the conditionsof further processing. Therefore, the resultant components preferablyhave a comparable inhomogeneity with regard to the distribution of thesmall particles or fragments thereof on the surface or in the interiorof the now fused large particles when the size of the further processedcomposite particles is used as the size scale for the assessment.

The invention also provides the sphere-shaped calcium carbonateparticles which can advantageously be used to produce the compositeparticles according to the invention, and the use thereof.

Thus, the present invention also concerns sphere-shaped calciumcarbonate particles which are obtainable by means of a method in which

a. a calcium hydroxide suspension is initially charged,

b. carbon dioxide or a carbon dioxide-containing gas mixture isintroduced into the suspension from step a. and

c. resultant calcium carbonate particles are separated off,

with 0.3% by weight to 0.7% by weight of at least oneaminotrisalkylenephosphonic acid being further added.

With regard to the preferred embodiment of said sphere-shaped calciumcarbonate particles and preferred methods for their production, theabove remarks apply mutatis mutandis.

Preferred application areas of the sphere-shaped calcium carbonateparticles encompass their use as additive for paper, plastics, paintsand/or varnishes, elastomers as well as adhesives and sealants, inconstruction chemistry, in dry mortar and in medical technology,especially as additive in resorbable polymers.

In this connection, what can be observed mutatis mutandis especially forcompositions comprising, based in each case on the total weight of thecomposition,

a) at least 0.1% by weight, preferably at least 0.2% by weight and inparticular at least 0.5% by weight to 50.0% by weight of at least onesphere-shaped calcium carbonate and

b) at least 0.1% by weight, preferably at least 0.2% by weight and inparticular at least 0.5% by weight to 50.0% by weight of at least onepolymer, preferably at least one thermoplastic polymer, particularlypreferably at least one resorbable polymer and in particular at leastone poly-D-, poly-L- and/or poly-D-L-lactic acid, are the advantages andeffects mentioned in this application, especially with regard to theimprovement of the mechanical properties and the acid stability of thecomposition. With regard to the preferred choice of polymer, the aboveremarks apply mutatis mutandis.

The present invention will be further illustrated below by means ofmultiple examples and comparative examples, without the intention ofrestricting the inventive concept as a result.

-   -   Materials used:        -   Granulate 1 (poly(L-lactide); inherent viscosity: 0.8-1.2            dL/g (0.1% in chloroform, 25° C.); Tg: 60-65° C.; Tm:            180-185° C.)        -   Granulate 2 (poly(L-lactide); inherent viscosity: 1.5-2.0            dL/g (0.1% in chloroform, 25° C.)); Tg: 60-65° C.;        -   Granulate 3 (poly(D,L-lactide); inherent viscosity: 1.8-2.2            dL/g (0.1% in chloroform, 25° C.)); Tg: 55-60° C.; amorphous            polymer without melting point    -   The average particle diameter of the polylactide granulates 1 to        3 was, in each case, within the range from 1 to 6 mm.

Within the context of the present examples, the following variables wereascertained as follows:

-   -   CaCO₃ content: The CaCO₃ content was ascertained by means of        thermogravimetry with an STA 6000 from Perkin Elmer under        nitrogen within the range from 40° C. to 1000° C. at a heating        rate of 20° C./min. In this connection, the weight loss was        determined between about 550° C. and 1000° C. and the CaCO₃        content in percent was calculated therefrom via a factor of        2.274 (CaCO₃:CO₂ molar mass ratio).    -   β-tricalcium phosphate content (β-TCP content): The β-TCP        content was ascertained by means of thermogravimetry with an STA        6000 from Perkin Elmer under nitrogen within the range from        40° C. to 1000° C. at a heating rate of 20° C./min. The        proportion by weight that remains at 1000° C. corresponds to the        β-TCP content in percent.    -   T_(P): The peak temperature T_(P) was ascertained by means of        thermogravimetry with an STA 6000 from Perkin Elmer under        nitrogen within the range from 40° C. to 1000° C. at a heating        rate of 20° C./min. The peak temperature of the first derivation        of the mass loss curve corresponds to the temperature with the        greatest mass loss in polymer degradation.    -   d₂₀, d₅₀, d₉₀: The particle-size distribution of the calcium        carbonate-containing composite powder was determined using laser        diffraction (HELOS measurement range R5 with RODOS dispersion        system from Sympatec). For the calcium carbonate powder, the        particle-size distribution was determined using the Sedigraph        5100 with MasterTech 51 from Micromeretics. The dispersion        solution used was 0.1% sodium polyphosphate solution (NPP).    -   Fraction <20 μm: Determination as for d₅₀. Evaluation of the        fraction <20 μm.    -   Moisture: The water content of the calcium carbonate-containing        composite powder was determined using a Karl Fischer coulometer        C30 from Mettler Toledo at 150° C. The water content of the        calcium carbonate powder was determined using the halogen        moisture analyzer HB43 from Mettler at 130° C. (amount weighed:        6.4-8.6 g of powder; measurement time: 8 minutes).    -   Inherent viscosity: Inherent viscosity (dL/g) was determined        using an Ubbelohde viscometer, capillary 0c, in chloroform at        25° C. and 0.1% polymer concentration.    -   Flowability: The flowability of the samples was assessed using        an electromotive film applicator from Erichsen. To this end, a        200 μm or 500 μm doctor blade was used. The application rate on        film type 255 (Leneta) was 12.5 mm/s. The assessment was as        follows: 1=very good; 2=good; 3=satisfactory; 4=adequate;        5=inadequate

Determination of the mechanical properties on injection-molded testpieces: Three-point bending strength and elastic modulus were determinedby means of the texture analyzer TA.XTplus (Stable Micro Systems,Godalming (UK)). The capacity of the load cell used was 50 kg. Exponent6.1.9.0 software was used. The measurement details are presented inTable 1 below:

TABLE 1 Stress device: Three-point stress in accordance with DIN EN843-1 Diameter of support/stress rolls: 5.0 mm Measurement: Inaccordance with DIN EN ISO 178 Support distance: 45.0 mm Test speed:0.02 mm/s Preliminary speed: 0.03 mm/s Recording of force and distanceTest pieces: Dimensions approx. 3 mm × 10 mm × 50 mm after production(injection-molding) Storage until measurement in desiccator at roomtemperature n ≥ 5

Test pieces were produced using the extruder HAAKE MiniLab II, orinjection-molding using the HAAKE MiniJet II. The process conditions inrelation to test-piece production are outlined in Table 2 below:

TABLE 2 Pressure, Temperature, Temperature, injection- Time,Temperature, injection- injection molding injection- Composite extruder[° C.] molding [° C.] mold [° C.] [bar] molding [s] Example 3 180 180 80700 10 Example 4 180 180 70 700 10 Example 5 185 185 80 700 10 Example 6195 195 80 700 10 Example 7 175 175 72 700 10 Comparison 1 175 175 70700 10

Cytotoxicity Test

The cytotoxicity test (FDA/GelRed) was carried out as follows: Thereference or negative control used was tissue culture polystyrene(TCPS). 4 replicates per sample and four TCPS (4×) as control were usedin each case.

Experimental Procedure:

-   1. The unsterile samples were provided in a 24-well microtiter    plate. In said plate, the samples and the TCPS platelets were    sterilized with 70% ethanol (undenatured) for 30 min, then rinsed    with 1×PBS (phosphate-buffered saline solution) for 2×30 min, and    subsequently equilibrated with sterile α-medium. Thereafter, the    samples were inoculated with MC3T3-E1 cells at an inoculation    density of 25 000 cells/cm² (50 000 cells/ml).

A partial medium exchange (1:2) was performed on day 2.

-   2. After 1 day and 4 days in cell culture, cytotoxicity was    determined.-   3. Viability staining was performed on day 1 and 4 according to the    standard protocol by means of a combination stain composed of FDA    and GelRed.-   4. The micrographs were generated on the Observer Z1m/LSM 700.

Objective: EC Plan-Neofluar 10×;

Images photographed with AxioCam HRc camera:

Excitation of green fluorescence: LED Colibri 470; filter set FS10(AF488)

Excitation of red fluorescence: LED Colibri 530; filter set FS14 (AF546)

Images captured in laser-scanning mode:

Track 1: Laser: 488 nm, DBS 560 nm, PMT1: 488-560 nm,

Track 2: Laser: 555 nm, DBS 565 nm, PMT2: 565-800 nm

-   5. The assessment was made according to the following cytotoxicity    scale:

Acceptance: the material is not cytotoxic (max. 5% dead cells)

Slight inhibition: the material is slightly toxic (5%-20% dead cells)

Distinct inhibition: the material is moderately toxic (20%-50% deadcells)

Toxicity: the material is highly cytotoxic (>50%-100% dead cells)

-   6. The cell counts are based on the section of image that was    photographed or scanned.

The results are outlined in Table 3.

Electron Microscope (SEM)

The scanning electron micrographs were obtained using a high-voltageelectron microscope (Zeiss, DSM 962) at 15 kV. The samples were sprayedwith a gold/palladium layer.

EXAMPLE 1 (REACTANT FOR COMPOSITE POWDER ACCORDING TO THE CLAIMEDINVENTION)

At a starting temperature of 10° C., a CO₂ gas mixture containing 20%CO₂ and 80% N₂ was introduced into a 4 L calcium hydroxide suspensionhaving a concentration of 75 g/L CaO. The gas flow rate was 300 L/h. Thereaction mixture was stirred at 350 rpm and the reaction heat wasdissipated during the reaction. Upon an abrupt drop in the conductance(drop of more than 0.5 mS/cm/min and decrease in the conductance by morethan 0.25 mS/cm within 30 seconds), 0.7% aminotris(methylenephosphonicacid), based on CaO (as theoretical reference value), is added to thesuspension. The reaction to yield the sphere-shaped calcium carbonateparticles was completed when the reaction mixture was quantitativelycarbonated to yield sphere-shaped calcium carbonate particles, thereaction mixture having then a pH between 7 and 9. In the present case,the reaction was completed after approximately 2 h and the reactionmixture had a pH of 7 at the end of the reaction.

The resultant sphere-shaped calcium carbonate particles were separatedoff and dried by conventional means. They had an average particlediameter of 12 μm. A typical SEM image is presented in FIG. 1.

EXAMPLE 2 (REACTANT FOR COMPOSITE POWDER ACCORDING TO THE CLAIMEDINVENTION)

500 mL of demineralized water were initially charged in a 1000 mLbeaker. 125 g of sphere-shaped calcium carbonate particles as perExample 1 were added under stirring and the resultant mixture wasstirred for 5 min. 37.5 g of a 10% sodium metaphosphate (NaPO₃)_(n)solution were added slowly and the resultant mixture was stirred for 10min. 75.0 g of 10% phosphoric acid were added slowly and the resultantmixture was stirred for 20 h. The precipitate is separated off and driedovernight at 130° C. in a drying cabinet. The resultant sphere-shapedcalcium carbonate particles likewise had an average particle diameter of12 μm.

An SEM image of the sphere-shaped calcium carbonate particles ispresented in FIG. 2. A thin phosphate layer can be identified on thesurface of the sphere-shaped calcium carbonate particles.

EXAMPLE 3 (COMPOSITE POWDER ACCORDING TO THE CLAIMED INVENTION)

A composite powder composed of sphere-shaped calcium carbonate particlesand a polylactide (PLLA) was produced following the method described inJP 62083029 A, using the instrument NHS-1. Cooling was carried out using12° C. cold water. A polylactide granulate 1 and the sphere-shapedcalcium carbonate particles from Example 1 were used as the motherparticles and as the baby particles (filler), respectively.

39.5 g of polylactide granulate were mixed with 26.3 g of CaCO₃ powderand filled at 6400 rpm. The rotor speed of the aggregate was adjusted to6400 rpm (80 m/s) and the metered materials were processed for 10 min.The maximally reached temperature in the grinding space of the NHS-1 was35° C. Altogether 7 repeats with the same amounts of material and samemachine settings were carried out. Altogether 449 g of composite powderwere obtained. The composite powder obtained was manually dry-sievedthrough a 250 μm sieve. The sieve residue (fraction >250 μm) was 0.4%.

An SEM image of the composite powder obtained is presented in FIG. 3 a.

Examples 4 to 7 (composite powder according to the claimed invention)Further composite powders were produced analogously to Example 3, thoughthe cooling was carried out at approx. 20° C. in Example 5. 30 g ofpolylactide granulate were mixed with 20 g of CaCO₃ powder in each case.The maximally reached temperature in the grinding space of the NHS-1 was33° C. for Example 4, 58° C. for Example 5, 35° C. for Example 6 and 35°C. for Example 7. The products were sieved in order to remove as far aspossible the coarse fraction >250 μm (manual dry sieving through a 250μm sieve). In Examples 4, 6 and 7, the fraction <20 μm was additionallyremoved as far as possible by flow classification (by means of airclassification) or by sieving (by means of an air-jet sieving machine).The materials used, the production procedure with or without sieving/airclassification and also the properties of the composite powders obtainedare outlined in Table 3 below.

FIG. 3a , FIG. 3b and FIG. 3c show an SEM image from Example 3 as wellas images of various doctor-blade applications (12.5 mm/s) from Example3 (FIG. 3 b: 200 μm doctor blade; FIG. 3 c: 500 μm doctor blade).

The SEM image of the composite powder obtained is presented in FIG. 3a .In contrast to the edged, irregular particle shape typical forcryogenically ground powders, the particles of the composite powderobtained have a round particle shape or high sphericity that is veryadvantageous for SLM methods. The PLLA surface is sparsely occupied bysphere-shaped calcium carbonate particles and fragments thereof. Thesample has a wide particle-size distribution with an increased finefraction.

The powder is flowable to a limited extent (FIGS. 3b and 3c ). A heap ofpowder is pushed ahead by the doctor blade. Owing to the limited flowbehavior, presumably caused by a relatively high proportion of fineparticles, only very thin layers are formed with both doctor blades.

FIG. 4a , FIG. 4b and FIG. 4c show an SEM image from Example 4 as wellas images of various doctor-blade applications (12.5 mm/s) from Example4 (FIG. 4 b: 200 μm doctor blade; FIG. 4 c: 500 μm doctor blade).

The SEM image of the composite powder obtained is presented in FIG. 4a .In contrast to the edged, irregular particle shape typical forcryogenically ground powders, the particles of the composite powderobtained have a round particle shape or high sphericity that is veryadvantageous for SLM methods. The PLLA surface is sparsely occupied bysphere-shaped calcium carbonate particles and fragments thereof. Thesample has a distinctly narrower particle-size distribution with littlefine fraction.

The powder is very highly flowable and blade-coatable (FIGS. 4b and 4c). The thin layers (200 μm) can be blade-coated, too, and are largelyfree of doctor-blade stripes (grooves). The powder layer blade-coated at500 μm is homogeneous, densely packed, smooth and free of doctor-bladestripes.

FIG. 5a , FIG. 5b and FIG. 5c show an SEM image from Example 5 as wellas images of various doctor-blade applications (12.5 mm/s) from Example5 (FIG. 5 b: 200 μm doctor blade; FIG. 5 c: 500 μm doctor blade). Thepowder is flowable to a limited extent. A heap of powder is pushed aheadby the doctor blade. Owing to the limited flow behavior, presumablycaused by a relatively high proportion of fine particles, only very thinlayers are formed with both doctor blades.

FIG. 6a , FIG. 6b and FIG. 6c show an SEM image from Example 6 as wellas images of various doctor-blade applications (12.5 mm/s) from Example6 (FIG. 6 b: 200 μm doctor blade; FIG. 6 c: 500 μm doctor blade). Thepowder is highly flowable and blade-coatable. The thin layers (200 μm)can be blade-coated, too. Individual doctor-blade stripes presumably dueto excessively coarse powder particles are identifiable. The powderlayer blade-coated at 500 μm is not quite densely packed, but is free ofdoctor-blade stripes.

FIG. 7a , FIG. 7b and FIG. 7c show an SEM image from Example 7 as wellas images of various doctor-blade applications (12.5 mm/s) from Example7 (FIG. 7 b: 200 μm doctor blade; FIG. 7 c: 500 μm doctor blade). Thepowder is flowable and blade-coatable. The thin layers (200 μm) can beblade-coated, too. They are not homogeneous and there are moredoctor-blade stripes. Somewhat limited flow behavior is presumablycaused by excessively coarse powder particles. The powder layerblade-coated at 500 μm is homogeneous and free of doctor-blade stripes.

Comparison 1 (Comparative Example)

Microstructured composite particles composed of sphere-shaped calciumcarbonate particles from Example 1 and an amorphous polylactide (PDLLA)were produced following the method described in JP 62083029 A, using theinstrument NHS-1. Cooling was carried out using 12° C. cold water. Apolylactide granulate 3 and the sphere-shaped calcium carbonateparticles from Example 1 were used as the mother particles and as thebaby particles, respectively.

39.5 g of polylactide granulate were mixed with 10.5 g of CaCO₃ powderand filled at 8000 rpm. The rotor speed of the aggregate was adjusted to8000 rpm (100 m/s) and the metered materials were processed for 1.5 min.The maximally reached temperature in the grinding space of the NHS-1 was71° C. Altogether 49 repeats with the same amounts of material and samemachine settings were carried out. Altogether 2376 g of structuredcomposite particles were obtained. The structured composite particlesobtained were manually dry-sieved through a 800 μm sieve for themeasurement of the particle-size distribution. The sieve residue(fraction >800 μm) was 47%.

The properties of the microstructured composite particles obtained areoutlined in Table 3 below.

FIG. 8a , FIG. 8b and FIG. 8c show an SEM image from Comparison 1 aswell as images of various doctor-blade applications (12.5 mm/s) fromComparison 1 (FIG. 8 b: 200 μm doctor blade; FIG. 8 c: 500 μm doctorblade). The powder is poorly flowable and cannot be blade-coated to formlayer thicknesses 200 or 500 μm thin. The excessively coarse, irregularparticles become stuck during blade-coating. What arise areinhomogeneous layers with highly frequent and pronounced doctor-bladestripes.

The SEM analysis shows that the surfaces of the structured compositepowders are sparsely occupied by sphere-shaped calcium carbonateparticles and fragments thereof. In comparison with Examples 3-7, theparticles have a more irregular particle geometry.

EXAMPLE 8 (COMPOSITE POWDER ACCORDING TO THE CLAIMED INVENTION)

A composite powder composed of β-tricalcium phosphate particles and apolylactide (PDLLA) was produced following the method described in JP62083029 A, using the instrument NHS-1. Cooling was carried out using12° C. cold water. A polylactide granulate 3 and β-tricalcium phosphate(β-TCP; d₂₀=30 μm; d₅₀=141 μm; d₉₀=544 μm) were used as the motherparticles and as the baby particles, respectively. The SEM image of theβ-TCP used are shown in FIG. 9a and FIG. 9 b.

30.0 g of polylactide granulate were mixed with 20.0 g of β-TCP powderand filled at 6400 rpm. The rotor speed of the aggregate was adjusted to6400 rpm (80 m/s) and the metered materials were processed for 10 min.Altogether 5 repeats with the same amounts of material and same machinesettings were carried out. Altogether 249 g of composite powder wereobtained. The product were sieved in order to remove as far as possiblethe coarse fraction >250 μm (manual dry sieving through a 250 μm sieve).Thereafter, the fine fraction <20 μm was separated off by means of anair-jet sieving machine via a 20 μm sieve.

EXAMPLE 9 (COMPOSITE POWDER ACCORDING TO THE CLAIMED INVENTION)

A composite powder composed of rhombohedral calcium carbonate particlesand a polylactide (PDLLA) was produced following the method described inJP 62083029 A, using the instrument NHS-1. Cooling was carried out using12° C. cold water. A polylactide granulate 3 and rhombohedral calciumcarbonate particles (d₂₀=11 μm; d₅₀=16 μm; d₉₀=32 μm) were used as themother particles and as the baby particles, respectively.

30.0 g of polylactide granulate were mixed with 20.0 g of therhombohedral calcium carbonate particles and filled at 6400 rpm. Therotor speed of the aggregate was adjusted to 6400 rpm (80 m/s) and themetered materials were processed for 10 min. Altogether 5 repeats withthe same amounts of material and same machine settings were carried out.Altogether 232 g of composite powder were obtained. The product weresieved in order to remove as far as possible the coarse fraction >250 μm(manual dry sieving through a 250 μm sieve). Thereafter, the finefraction <20 μm was separated off by means of an air-jet sieving machinevia a 20 μm sieve.

EXAMPLE 10 (COMPOSITE POWDER ACCORDING TO THE CLAIMED INVENTION)

A composite powder composed of ground calcium carbonate particles and apolylactide (PDLLA) was produced following the method described in JP62083029 A, using the instrument NHS-1. Cooling was carried out using12° C. cold water. A polylactide granulate 3 and ground calciumcarbonate (GCC; d₂₀=15 μm; d₅₀=46 μm; d₉₀=146 μm) were used as themother particles and as the baby particles, respectively.

30.0 g of polylactide granulate were mixed with 20.0 g of GCC and filledat 6400 rpm. The rotor speed of the aggregate was adjusted to 6400 rpm(80 m/s) and the metered materials were processed for 10 min. Altogether5 repeats with the same amounts of material and same machine settingswere carried out. Altogether 247 g of composite powder were obtained.The product were sieved in order to remove as far as possible the coarsefraction >250 μm (manual dry sieving through a 250 μm sieve).Thereafter, the fine fraction <20 μm was separated off by means of anair-jet sieving machine via a 20 μm sieve.

TABLE 3 Example 3 Example 4 Example 5 Example 6 Example 7 Comparison 1Composition for the production of the composite powder comprisingmicrostructured particles m(Example 1) 40 40 0 40 40 20 [% by weight]m(Example 2) 0 0 40 0 0 0 [% by weight] Polylactide Granulate 1Granulate 1 Granulate 1 Granulate 2 Granulate 3 Granulate 3m(Polylactide) 60 60 60 60 60 80 [% by weight] Production of thecomposite powder comprising microstructured particles Sieving <250 μm<250 μm <250 μm <250 μm <250 μm <800 μm  <20 μm  <20 μm  <20 μm (onlyfor measurement (air classification) (air-jet sieving) (air-jet sieving)of the particle-size distribution) CaCO₃ content 41.0 22.4 35.0 19.522.3 22.4 (average from [% by weight]¹ 5 measurements) T_(P) [° C.]¹ 291310 341 304 286 319 (average from 5 measurements) d₅₀ [μm]¹ 25 47 26 112136 228 Fraction < 20 μm 43.6 13.7 37.7 0.3 2.3 20.6 [% by volume]¹ d₂₀[μm]¹ 9 26 14 69 80 d₉₀ [μm]¹ 86 102 70 223 247 d₂₀/d₅₀ [%] 36 52 54 6259 Moisture 0.8 0.6 0.5 0.9 0.9 0.3 [% by weight]¹ Inherent viscosity1.0 1.0 0.9 1.9 1.9 1.9 [dL/g] Three-point bending 66 68 77 84 67 79strength [MPa] Elastic modulus 4782 3901 4518 3530 3594 3420 [N/mm²]Flowability 4 1 4 2 3 5 Cytotoxicity test not cytotoxic not cytotoxicnot cytotoxic — not cytotoxic not cytotoxic Example 8 Example 9 Example10 Composition for the production of the composite powder comprisingmicrostructured particles m(Filler) 40 40 40 [% by weight] PolylactideGranulate 3 Granulate 3 Granulate 3 m(Polylactide) 60 60 60 [% byweight] Production of the composite powder comprising microstructuredparticles Sieving <250 μm <250 μm <250 μm  <20 μm  <20 μm  <20 μmAir-jet sieving Air-jet sieving Air-jet sieving Filler content 24.9 24.226.6 [% by weight]* T_(P) [° C.] 341° C.  303° C.  303° C.  d₂₀ [μm] 8574 75 d₅₀ [μm] 131 128 120 d₉₀ [μm] 226 257 230 Fraction < 20 μm 3.0 4.51.6 [% by volume] Moisture 0.6 0.6 0.6 [% by weight] Inherent viscosity1.8 1.8 1.9 [dL/g] ¹at least duplicate determination

Comparison 2, Example 11 (composite powder according to the claimedinvention), Example 12 (composite powder according to the claimedinvention), Example 13 (composite powder according to the claimedinvention), Example 14 (composite powder according to the claimedinvention) and Example 15 PLA pellets were mixed and melted as purepellets and with 4 different fillers (25% by weight) using a BrabenderPlasti-Corder. The chamber temperature was 190° C. at a rotational speedof 50 rpm. Pellets and filler powder were mixed for 5 minutes;thereafter, approx. 16 g of the mixture were pressed in a hydraulicpress at a pressure of 0.96-1.2 MPa for 5 minutes.

In all the examples, the polymer used was PLA (NatureWorks Ingeo TMBiopolymer 3251 D). In Comparison 2, no calcium carbonate particles wereadded. In Example 11, calcium carbonate particles according to Example 1were added. In Example 12, calcium carbonate particles according toExample 2 were added. In Example 13, calcium carbonate particles wereadded, the particles having been produced analogously to Example 2 butwithout addition of phosphoric acid. In Example 14, calcium carbonateparticles were added, the particles having been produced analogously toExample 2 but without addition of sodium metaphosphate (NaPO₃)_(n)). InExample 15, stearic acid-coated calcium carbonate particles obtained byconventional means were added.

Characterization of the PLA composites of Comparison 2 and Example 11-15

a) Mechanical properties

The mechanical properties of PLA and of the composites were tested usingthe universal testing machine UTM 1445 from Zwick/Roell. The tensilestrength, the elastic modulus and the stretch of the materials weredetermined here. The test speed was 10 mm/min at a measurement length of50 mm.

b) Thermal properties

The thermal stability of the samples was determined by means ofthermogravimetry. The thermogravimetric measurements were carried outusing an STA 6000 from Perkin Elmer under nitrogen within the range from40° C. to 1000° C. at a heating rate of 20° C./min.

c) Optical assessment of the samples (**grades of 1-3)

1=transparent pure polymer; no identifiable discoloration due to thermaldegradation

2=white polymer compound; change in color to white due to addition ofthe filler; no identifiable discoloration due to thermal degradation

3=brown color due to thermal degradation of the compound

The addition of the CaCO₃ particles to the PLA matrix led to a change incolor from transparent pure PLA to white composites for all the fillersexcept for Example 15. In the case of the sample with stearicacid-coated calcium carbonate particles, the color changed to a lightbrown, indicating polymer degradation. All the other samples show nosigns of degradation at all.

The observed properties are outlined in Table 4.

TABLE 4 Comparison 2 Example 11 Example 12 Example 13 Example 14 Example15 CaCO₃ particles Example 1 Example 2 Example 2 Example 2 Coated withwithout without stearic acid addition of addition of (1.0%) phosphoricsodium acid metaphosphate pH ¹⁾ (immediately/24 h) 10.0/10.0 6.1/6.28.9/9.0 7.0/7.0 — Moisture [%] 0.1 0.1 0.1 0.1 0.1 d₅₀ [μm] 12.1 12.212.0 14.3 14.2 Spec. surface area [m²/g] 1.1 0.2 0.6 0.9 4.9 P₂O₅content [%] 0.3 3.1 0.4 6.8 — Qualitative phase analysis Calcite CalciteCalcite Calcite + brushite Tensile strength [MPa] 47.99 44.57 40.5640.20 37.95 41.39 Elastic modulus [MPa] 1345.0 1680.4 1718.9 1601.91625.8 1627.1 Onset temperature (TGA) [° C.] 348.8 326.1 360.3 337.4358.4 322.9 Peak temperature (TGA) [° C.] 377.6 356.5 380.3 368.1 380.8354.5 Grading of test pieces** 1 2 2 2 2 3

1. A composite powder containing microstructured particles obtainable bymeans of a method in which large particles are combined with smallparticles, wherein the large particles have an average particle diameterwithin the range from 0.1 μm to 10 mm, the large particles comprise atleast one polymer, the small particles are arranged on the surface ofthe large particles and/or distributed inhomogeneously within the largeparticles, the small particles comprise sphere-shaped precipitatedcalcium carbonate particles having an average diameter within the rangefrom 0.05 μm to 50.0 μm, characterized in that the sphere-shaped calciumcarbonate particles are obtainable by means of a method in which a. acalcium hydroxide suspension is initially charged, b. carbon dioxide ora carbon dioxide-containing gas mixture is introduced into thesuspension from step a. and c. resultant calcium carbonate particles areseparated off, with 0.3% by weight to 0.7% by weight of at least oneaminotrisalkylenephosphonic acid being further added, and the particlesof the composite powder have an average particle size d₅₀ within therange from 10 μm to less than 200 μm.
 2. The composite powder as claimedin claim 1, comprising calcium carbonate particles obtainable by meansof a method in which aminotrismethylenephosphonic acid,aminotrisethylenephosphonic acid, aminotrispropylenephosphonic acidand/or aminotrisbutylenephosphonic acid are added.
 3. The compositepowder as claimed in claim 1, comprising calcium carbonate particlesobtainable by means of a method in which the carbon dioxide or thecarbon dioxide-containing gas mixture is introduced until the reactionmixture has a pH less than
 9. 4. The composite powder as claimed inclaim 1, comprising calcium carbonate particles obtainable by means of amethod in which the conversion of the calcium hydroxide suspension withthe carbon dioxide or the carbon dioxide-containing gas mixture iscarried out at a temperature less than 25° C.
 5. The composite powder asclaimed in claim 1, comprising calcium carbonate particles obtainable bymeans of a method in which carbon dioxide or a carbon dioxide-containinggas mixture is introduced into the calcium hydroxide suspension at a gasflow rate within the range from 0.02 L CO₂/(h*g Ca(OH)₂) to 2.0 LCO₂/(h*g Ca(OH)₂).
 6. The composite powder as claimed in claim 1,characterized in that the sphere-shaped calcium carbonate particles havean average diameter less than 30.0 μm, especially less than 20.0 μm. 7.The composite powder as claimed in claim 1, characterized in that thesphere-shaped calcium carbonate particles have a size distribution inwhich at least 90.0% by weight of all calcium carbonate particles have aparticle diameter within the range of average particle diameter −30% toaverage particle diameter +30%.
 8. The composite powder as claimed inclaim 1, characterized in that the sphere-shaped calcium carbonateparticles have a shape factor, defined as the quotient formed fromminimum particle diameter and maximum particle diameter, greater than0.90.
 9. The composite powder as claimed in claim 1, characterized inthat the large particles comprise at least one thermoplastic polymer.10. The composite powder as claimed in claim 1, characterized in thatthe large particles comprise at least one resorbable polymer.
 11. Thecomposite powder as claimed in claim 10, characterized in that theresorbable polymer has an inherent viscosity, measured in chloroform at25° C. and 0.1% polymer concentration, within the range from 0.3 dL/g to8.0 dL/g.
 12. The composite powder as claimed in claim 1, characterizedin that the large particles comprise poly-D-, poly-L- and/orpoly-D,L-lactic acid.
 13. The composite powder as claimed in claim 1,characterized in that the large particles comprise at least oneresorbable polyester having a number-average molecular weight within therange from 500 g/mol to 1 000 000 g/mol.
 14. The composite powder asclaimed in claim 1, characterized in that the large particles compriseat least one polyamide.
 15. The composite powder as claimed in claim 1,characterized in that the large particles comprise at least onepolyurethane.
 16. The composite powder as claimed in claim 1,characterized in that the proportion by weight of the precipitatedcalcium carbonate particles, based on the total weight of the compositepowder, is at least 0.1% by weight.
 17. The composite powder as claimedin claim 1, characterized in that the composite powder comprise, basedon the total weight of the composite powder, 40.0% by weight to 80.0% byweight of PLLA and 20.0% by weight to 60.0% by weight of precipitatedcalcium carbonate particles.
 18. A method comprising adding compositepowder as claimed in claim 1 as additive, especially as polymeradditive, as additive substance or starting material for compounding,for the production of components, for applications in medical technologyand/or in microtechnology and/or for the production of foamed articles.19. A component obtainable by selective laser sintering of a compositioncomprising a composite powder as claimed in claim 1, except for implantsfor uses in the field of neurosurgery, oral surgery, jaw surgery, facialsurgery, neck surgery, nose surgery and ear surgery as well as handsurgery, foot surgery, thorax surgery, rib surgery and shoulder surgery.20. Sphere-shaped calcium carbonate particles obtainable by means of amethod in which a. a calcium hydroxide suspension is initially charged,b. carbon dioxide or a carbon dioxide-containing gas mixture isintroduced into the suspension from step a. and c. resultant calciumcarbonate particles are separated off, with 0.3% by weight to 0.7% byweight of at least one aminotrisalkylenephosphonic acid being furtheradded.
 21. A method comprising adding the sphere-shaped calciumcarbonate particles as claimed in claim 20 as additive for paper,plastics, paints, varnishes, elastomers, adhesives, sealants, inconstruction chemistry, in dry mortar and in medical technology, or inresorbable polymers.